What is Red? Physics and optics

Red is the colour at the longer-wavelengths end of the spectrum of visible light next to orange, at the opposite end from violet. Red colour has a predominant light wavelength of roughly 620–740 nanometers. Light with a longer wavelength than red but shorter than terahertz radiation and microwave is called infrared – this cannot be seen by human eyes, although it can be sensed as heat. In terms of optics, red is the color evoked by light that stimulates neither the S or the M (short and medium wavelength) cone cells of the retina, combined with a fading stimulation of the L (long-wavelength) cone cells.

Red is one of the additive primary colours of visible light, along with green and blue, which in Red Green Blue (RGB) color systems are combined to create all the colors on a computer monitor or television screen. Red is also one of the subtractive primary colours, along with yellow and blue, of the RYB colour space and traditional colour wheel used by painters and artists.

Reds can vary in shade from very light pink to very dark maroon or burgundy; and in hue from the bright orange-red scarlet or vermilion to the bluish-red crimson.

In complete contrast to the restrained qualities of blue, red is visually one of the most insistent, powerful colours, and immediately attracts attention. When set against cooler colours, green in particular, red advances towards the
viewer. It has considerable kinetic energy. In contrast to the transparency and luminosity of yellow, red is relatively dense and solid.

Etymology and definitions

The word red is derived from the Old English rēad. The word can be further traced to the Proto-Germanic rauthaz and the Proto-Indo European root rewdʰ-. In Sanskrit, the word rudhira means red or blood. In the Akkadian language of Ancient Mesopotamia and in the modern Inuit language of Inuit, the word for red is the same word as “like blood”.

The words for ‘colored’ in Latin (coloratus) and Spanish (colorado) both also mean ‘red.’In Portuguese the word for red is vermelho, which comes from Latin “vermiculus“, meaning “little worm”.

In the Russian language, the word for red, Кра́сный (krasniy), comes from the same old Slavic root as the words for “beautiful”—красивый (krasiviy) and “excellent”—прекрасный (prekrasniy). Thus Red Square in Moscow, named long before the Russian Revolution, meant simply “Beautiful Square”.

Pigments

Red, black and white were the first colours used by artists in the Upper Paleolithic age, probably because natural pigments such as red ochre and iron oxide were readily available where early people lived.

Red Ochre – a clay colored red by iron oxide: Inside cave 13B at Pinnacle Point, an archeological site found on the coast of South Africa, paleoanthropologists in 2000 found evidence that, between 170,000 and 40,000 years ago, Late Stone Age people were scraping and grinding ochre, probably with the intention of using it to colour their bodies. The cave of Altamira in Spain has a painting of a bison coloured with red ochre that dates to between 15,000 and 16,500 BC.

Mars Red: a synthetic red ochre, the color of the very first natural red pigment, invented in the late 19th and early 20th century in the German chemical industry.

Red hematite powder was also found scattered around the remains at a grave site in a Zhoukoudian cave complex near Beijing. The site has evidence of habitation as early as 700,000 years ago. The hematite might have been used to symbolize blood in an offering to the dead.

Madder/alizarin made from the root of rubia tinctorum which grew widely in Europe, Africa and Asia. This colour leaned toward orange/brick-red, and faded easily in the sun or during washing. In 1826, the French chemist Pierre-Jean Robiquet discovered the organic compound alizarin, the powerful coloring ingredient of the madder root. In 1868, German chemists Carl Graebe and Liebermann were able to synthesize alizarin, and to produce it from coal tar. The synthetic red was cheaper and more lasting than the natural dye, and the plantation of madder in Europe and import of cochineal from Latin America soon almost completely ceased.

Kermes/Carmine/Vermillion/Cochineal: red dye was made made from the carminic acid in tiny female scale insects in the genus Kermes. The insects were gathered, dried, crushed, and boiled with different ingredients in a long and complicated process, which produced a brilliant scarlet. The different species feed on different trees and plant parts and produce reds of varying brilliance, and hence value.

• Kermes vermilio lived on the sap and leaves of oak trees in Eastern Europe and around the Mediterranean.   Jars of kermes have been found in a Neolithic cave-burial at Adaoutse, Bouches-du-Rhône. Kermes from oak trees was later used by Romans, who imported it from Spain. Kermes is also mentioned in the Bible.
• For those with even more money there was Polish Cochineal; also known as Kermes vermilio or “Blood of Saint John”, which was made from a related insect, the Margodes polonicus. It made a more vivid red than ordinary Kermes.
• Cochineal  (also known as Persian kirmiz) was the finest and most expensive variety of red made from Porphyrophora hamelii (Armenian cochineal) which lived on the roots and stems of certain grasses. It is mentioned in texts as early as the 8th century BC, and it was used by the ancient Assyrians and Persians.
• Mexican cochineal used by the Aztecs lived on cactus plants, closely related to the Kermes varieties of Europe, but it could be harvested several times a year, and it was ten times stronger than the Kermes of Poland.

Cinnabar: a mineral – a common ore of mercury. It was one of the finest reds of ancient times – the paintings have retained their brightness for more than twenty centuries. The source of cinnabar for the Romans was a group of mines near Almadén, southwest of Madrid, in Spain. Working in the mines was extremely dangerous, the miners were slaves or prisoners, and being sent to the cinnabar mines was a virtual death sentence.

Red lead or Lead tetroxide pigment also called minium, used as the red in Persian and Indian miniature paintings as well as in European art

Brazilin was another popular red dye in the Middle Ages. It came from the Sapanwood tree, which grew in India, Malaysia and Sri Lanka. A similar tree, brazilwood, grew on the coast of South America. The red wood was ground into sawdust and mixed with an alkaline solution to make dye and pigment. It became one of the most profitable exports from the New World, and gave its name to the nation of Brazil.

Red lac, also called red lake, crimson lake or carmine lake, was an important red pigment in Renaissance and Baroque art. Since it was translucent, thin layers of red lac were built up or glazed over a more opaque dark color to create a particularly deep and vivid color. Unlike vermilion or red ochre, made from minerals, red lake pigments are made by mixing organic dyes, made from insects or plants, with white chalk or alum. Red lac was made from the gum lac, the dark red resinous substance secreted by various scale insects, particularly the Laccifer lacca from India. Carmine lake was made from the cochineal insect from Central and South America, Kermes lake came from a different scale insect, kermes vermilio, which thrived on oak trees around the Mediterranean. Other red lakes were made from the rose madderplant and from the brazilwood tree. Red lake pigments were an important part of the palette of 16th century Venetian painters, particularly Titian, but they were used in all periods.Since the red lakes were made from organic dyes, they tended to be fugitive, becoming unstable and fading when exposed to sunlight.

Venetian red, which was considered the most expensive and finest red in Europe. Its secret ingredient was arsenic, which brightened the color.

Turkey red, known in France as rouge d’Adrinople. Beginning in the 1740s, this bright red colour was used to dye or print cotton textiles in England, the Netherlands and France. Turkey red used madder as the colourant, but the process was longer and more complicated, involving multiple soaking of the fabrics in lye, olive oil, sheep’s dung, and other ingredients. The fabric was more expensive but resulted in a fine bright and lasting red, similar to carmine, perfectly suited to cotton. The fabric was widely exported from Europe to Africa, the Middle East and America. In 19th century America, it was widely used in making the traditional patchwork quilt.

Cadmium Red: synthetic red pigments, the colour of natural vermilion, invented in the late 19th and early 20th century by the German chemical industry.

Symbolism

Red has many different symbolic connotations – probably more than any other colour. As the colour of blood, it has historically been associated with sacrifice, danger and courage. Modern surveys in the United States and Europe show red is also the colour most commonly associated with heat, activity, passion, sexuality, anger, love and joy. In China and many other Asian countries it is the colour of happiness.

Egypt

In ancient Egypt, red was associated with life, health, and victory. Egyptians would colour themselves with red ochre during celebrations. Egyptian women used red ochre as a cosmetic to redden cheeks and lips and also used henna to colour their hair and paint their nails.

But, like many colours, it also had a negative association, with heat, destruction and evil. A prayer to god Isis said: “Oh Isis, protect me from all things evil and red.”The ancient Egyptians began manufacturing pigments in about 4000 BC.

Red ochre was widely used as a pigment for wall paintings, particularly as the skin colour of men. An ivory painter’s palette found inside the tomb of King Tutankhamun had small compartments with pigments of red ochre and five other colours. The Egyptians used the root of the rubia, or madder plant, and also used it to colour white power to use as a pigment

China

In China, red (simplified Chinese: 红; traditional Chinese: 紅; pinyin: hóng) is the symbol of fire and the south (both south in general and Southern China specifically).  Red has been an important colour in Chinese culture, religion, industry, fashion and court ritual since ancient times. It carries a largely positive connotation, being associated with courage, loyalty, honour, success, fortune, fertility, happiness, passion, and summer.

In Ancient China, artisans were making red and black painted pottery as early as the Yangshao Culture period (5000-3000 BC). A red-painted wooden bowl was found at a Neolithic site in Yuyao, Zhejiang. Other red-painted ceremonial objects have been found at other sites dating to the Spring and Autumn period (770–221 BC).

Silk was woven and dyed with red as early as the Han Dynasty (25–220 BC).

During the Han dynasty (200 BC to 200 AD) Chinese craftsmen made a red pigment, lead tetroxide, which they called ch-ien tan, by heating lead white pigment. Like the Egyptians, they made a light red dye from the madder plant to color silk fabric for gowns and used pigments colored with madder to make red lacquerware.

During the Tang dynasty new dyes and pigments were discovered. The Chinese used several different plants to make red dyes, including the flowers of carthamus tinctorius, the thorns and stems of a variety of sorghum plant called Kao-liang, and the wood of the sappanwood tree. For pigments, they used cinnabar, which produced the famous vermillion or “Chinese red” of Chinese laquerware.

Red played an important role in Chinese philosophy. It was believed that the world was composed of five elements: metal, wood, water, fire and earth, and that each had a color. Red was associated with fire. Each Emperor chose the color that his fortune-tellers believed would bring the most prosperity and good fortune to his reign. During the Zhou, Han, Jin, Song and Ming Dynasties, red considered a noble color, and it was featured in all court ceremonies, from coronations to sacrificial offerings, and weddings.

Red was also a badge of rank. During the Song dynasty (906–1279), officials of the top three ranks wore purple clothes; those of the fourth and fifth wore bright red; those of the sixth and seventh wore green; and the eighth and ninth wore blue. Red was the color worn by the royal guards of honor, and the color of the carriages of the imperial family. When the imperial family traveled, their servants and accompanying officials carried red and purple umbrellas. Of an official who had talent and ambition, it was said “he is so red he becomes purple.”

Red was also featured in Chinese Imperial architecture. In the Tang and Song Dynasties, gates of palaces were usually painted red, and nobles often painted their entire mansion red. One of the most famous works of Chinese literature, A Dream of Red Mansions by Cao Xueqin (1715–1763), was about the lives of noble women who passed their lives out of public sight within the walls of such mansions. In later dynasties red was reserved for the walls of temples and imperial residences. When the Manchu rulers of the Qing Dynasty conquered the Ming and took over the Forbidden City and Imperial Palace in Beijing, all the walls, gates, beams and pillars were painted in red and gold.

Red is not often used in traditional Chinese paintings, which are usually black ink on white paper with a little green sometimes added for trees or plants; but the round or square seals which contain the name of the artist are traditionally red.

 In Chinese cultural traditions, red is associated with weddings (where brides traditionally wear red dresses) and red paper is frequently used to wrap gifts of money or other objects. Special red packets (simplified Chinese: 红包;traditional Chinese: 紅包; pinyin: hóng bāo in Mandarin or lai see in Cantonese) are specifically used during Chinese New Year celebrations for giving monetary gifts.

On the more negative side, obituaries are traditionally written in red ink, and to write someone’s name in red signals either cutting them out of one’s life, or that they have died.

Red is also associated with either the feminine or the masculine (yin and yang respectively), depending on the source.

The Little Red Book, a collection of quotations from Chairman Mao Tse-Tung, founding father of the People’s Republic of China (PRC), was published in 1966 and widely distributed thereafter.

Japan

• In the Shinto religion of Japan, the gateways of temples, called torii, are traditionally painted vermilion red and black. The torii symbolizes the passage from the profane world to a sacred place. The bridges in the gardens of Japanese temples are also painted red (and usually only temple bridges are red, not bridges in ordinary gardens), since they are also passages to sacred places.
• Red was also considered a color which could expel evil and disease.
• In Japan, red is a traditional color for a heroic figure.

South Asia and Iran

Red lead or Lead tetroxide pigment was widely used as the red in Persian and Indian miniature paintings. 

• In India, the rubia plant has been used to make dye since ancient times. A piece of cotton dyed with rubia dated to the third millennium BC was found at an archaeological site at Mohenjo-daro. It has been used by Indian monks and hermits for centuries to dye their robes.
  • In Buddhism, red is one of the five colours which are said to have emanated from the Buddha when he attained enlightenment, or nirvana. It is particularly associated with the benefits of the practice of Buddhism; achievement, wisdom, virtue, fortune and dignity. It was also believed to have the power to resist evil. In China red was commonly used for the walls, pillars, and gates of temples.
  • The early Ottoman Turks led by the first Ottoman Sultan, Osman I, carried red banners symbolizing sovereignty, Ghazis and Sufism, until, according to legend, he saw a new red flag in his dream inlaid with a crescent.
  • In India it is also the colour of wealth, beauty, and the goddess Lakshmi.
  • In the Indian subcontinent, red symbolizes joy and good fortune. Brides traditionally wear a red sari, called the sari of blood, offered by their father, signifying that his duties as a father are transferred to the new husband, and as a symbol of his wish for her to have children. The colour is associated with purity, as well as with sexuality in marital relationships through its connection to heat and fertility. It is the symbolic colour for married women – for example the red dot in the middle of the forehead or in the hair parting.Once married, the bride will wear a sari with a red border, changing it to a white sari if her husband dies. In Pakistan and India, brides traditionally also have their hands and feet painted red with henna by the family of their new spouse, to bring happiness and signify their new status.

Africa

• In Central Africa, Ndembu warriors rub themselves with red paint during celebrations. Since their culture sees the colour as a symbol of life and health, sick people are also painted with it. Like most Central African cultures, the Ndembu see red as ambivalent, better than black but not as good as white.
• In other parts of Africa, however, red is a colour of mourning, representing death. Because red bears are associated with death in many parts of Africa, the Red Cross has changed its colours to green and white in parts of the continent.

Americas

The early inhabitants of America had their own vivid crimson dye, made from the cochineal, an insect of the same family as the Kermes of Europe and the Middle East, which feeds on the Opuntia, or prickly pear cactus plant. Red-dyed textiles from the Paracas culture (800–100 BC) have been found in tombs in Peru.

Red also featured in the burials of royalty in the Maya city-states. In the Tomb of the Red Queen inside Temple XIII in the ruined Maya city of Palenque, (600–700 AD), the skeleton and ceremonial items of a noble woman were completely covered with bright red powder made from cinnabar.

Western traditions

Greece

In ancient Greece and the Minoan civilization of ancient Crete, red was widely used in murals and in the polychrome decoration of temples and palaces. The Greeks began using red lead as a pigment.

Rome

Red had an important religious symbolism.

• In Roman mythology red is associated with the god of war, Mars. Red was used to colour statues and the skin of gladiators.Red was also the colour associated with army; Roman soldiers wore red tunics, and officers wore a cloak called a paludamentum which, depending upon the quality of the dye, could be crimson, scarlet or purple. The vexilloid of the Roman Empire had a red background with the letters SPQR in gold. A Roman general receiving a triumph had his entire body painted red in honour of his achievement.
• Romans wore togas with red stripes on holidays
• the bride at a wedding wore a red shawl, called a flammeum.
• Many Roman villas were decorated with vivid red murals – using vermilion from the mineral cinnabar.

Byzantium

After the fall of the Western Roman Empire, the Byzantine Empire, the princes of Europe and the Roman Catholic Church adapted red as a color of majesty and authority. It also played an important part in the rituals of the Catholic Church – it symbolized the blood of Christ and the Christian martyrs – and it associated the power of the kings with the sacred rituals of the Church.

Red was the colour of the banner of the Byzantine emperors. In Western Europe, Emperor Charlemagne painted his palace red as a very visible symbol of his authority, and wore red shoes at his coronation. Kings, princes and, beginning in 1295, Roman Catholic cardinals began to wear red coloured habitus.

When Abbe Suger rebuilt Saint Denis Basilica outside Paris in the early 12th century, he added stained glass windows coloured blue cobalt glass and red glass tinted with copper. Together they flooded the basilica with a mystical light. Soon stained glass windows were being added to cathedrals all across France, England and Germany. In Medieval painting red was used to attract attention to the most important figures; both Christ and the Virgin Mary were commonly painted wearing red mantles.

Red clothing was a sign of status and wealth. It was worn not only by cardinals and princes, but also by merchants, artisans and townspeople, particularly on holidays or special occasions. Red dye for the clothing of ordinary people was made from the the madder plant. The wealthy and aristocrats wore scarlet clothing dyed with kermes.

16th and 17th centuries

In Renaissance painting, red was used to draw the attention of the viewer; it was often used as the colour of the cloak or costume of Christ, the Virgin Mary, or another central figure. In Venice, Titian was the master of fine reds, particularly vermilion; he used many layers of pigment mixed with a semi-transparent glaze, which let the light pass through, to create a more luminous colour.

During the Renaissance trade routes were opened to the New World, to Asia and the Middle East, and new varieties of red pigment and dye were imported into Europe, usually through Venice, Genoa or Seville, and Marseille. Venice was the major depot importing and manufacturing pigments for artists and dyers from the end of the 15th century; the catalog of a Venetian Vendecolori, or pigment seller, from 1534 included vermilion and kermes.

There were guilds of dyers who specialized in red in Venice and other large Europeans cities. The pigment and dye merchants of Venice imported and sold all of these products and also manufactured their own color, called Venetian red.

Early in the 16th century, a brilliant new red was discovered in the Aztec Empire by Spanish conquistador Hernán Cortés in 1519-1521, they discovered slowly that  It worked particularly well on silk, satin and other luxury textiles. In 1523 Cortes sent the first shipment to Spain. Soon cochineal began to arrive in European ports aboard convoys of Spanish galleons. At first the guilds of dyers in Venice and other cities banned cochineal to protect their local products, but the superior quality of cochineal dye made it impossible to resist. By the beginning of the 17th century it was the preferred luxury red for the clothing of cardinals, bankers, courtesans and aristocrats.

The painters of the early Renaissance used two traditional lake pigments, made from mixing dye with either chalk or alum, kermes lake, made from kermes insects, and madder lake, made from the rubia tinctorum plant. With the arrival of cochineal, they had a third, carmine, which made a very fine crimson, though it had a tendency to change color if not used carefully. It was used by almost all the great painters of the 15th and 16th centuries, including Rembrandt, Vermeer, Rubens, Anthony van Dyck, Diego Velázquez and Tintoretto. Later it was used by Thomas Gainsborough, Seurat and J.M.W. Turner.

18th and 19th centuries

During the French Revolution, Red became a symbol of liberty and personal freedom used by the Jacobins and other more radical parties. Many of them wore a red Phrygian cap, or liberty cap, modeled after the caps worn by freed slaves in Ancient Rome. During the height of the Reign of Terror, women wearing red caps gathered around the guillotine to celebrate each execution. They were called the “Furies of the guillotine”. The guillotines used during the Reign of Terror in 1792 and 1793 were painted red, or made of red wood. During the Reign of Terror a statue of a woman titled liberty, painted red, was placed in the square in front of the guillotine. After the end of the Reign of Terror, France went back to the blue, white and red tricolor, whose red was taken from the traditional color of Saint Denis, the Christian martyr and patron saint of Paris.

In the mid-19th century, red became the color of a new political and social movement, socialism. It became the most common banner of the worker’s movement, of the French Revolution of 1848, of the Paris Commune in 1870, and of socialist parties across Europe.

As the Industrial Revolution spread across Europe, chemists and manufacturers sought new red dyes that could be used for large-scale manufacture of textiles. Turkey red was imported into Europe from Turkey and India in the 18th and early 19th century, later synthetic Alizarin was discovered.

The 19th century also saw the use of red in art to create specific emotions, not just to imitate nature, and particularly the study of how complementary colours such as red and green reinforced each other when they were placed next to each other.  Describing his painting, The Night Cafe, to his brother Theo in 1888, Van Gogh wrote: “I sought to express with red and green the terrible human passions. The hall is blood red and pale yellow, with a green billiard table in the center, and four lamps of lemon yellow, with rays of orange and green. Everywhere it is a battle and antithesis of the most different reds and greens.”

20th and 21st century

Revolution: In the 20th century, red was the colour of Revolution; it was the color of the Bolshevik Revolution in 1917 and of the Chinese Revolution of 1949, and later of the Cultural Revolution. Red was the colour of Communist Parties from Eastern Europe to Cuba to Vietnam.

Henri Matisse (1869–1954) was one of the first prominent painters to use the new cadmium red. He even tried, without success, to persuade the older and more traditional Renoir, his neighbour in the south of France, to switch from vermilion to cadmium red. Matisse was also one of the first 20th-century artists to make colour the central element of the painting, chosen to evoke emotions. “A certain blue penetrates your soul”, he wrote. “A certain red affects your blood pressure.”

Mark Rothko (1903–1970) also used red, in even simpler form, in blocks of dark, somber colour on large canvases, to inspire deep emotions. Rothko observed that colour was “only an instrument;” his interest was “in expressing human emotions tragedy, ecstasy, doom, and so on.” Rothko also began using the new synthetic pigments, but not always with happy results. In 1962 he donated to Harvard University a series of large murals of the Passion of Christ whose predominant colours were dark pink and deep crimson. He mixed mostly traditional colours to make the pink and crimson; synthetic ultramarine, cerulean blue, and titanium white, but he also used two new organic reds, Naphtol and Lithol. The Naphtol did well, but the Lithol slowly changed color when exposed to light. Within five years the deep pinks and reds had begun to turn light blue, and by 1979 the paintings were ruined and had to be taken down.

Western Symbolism

Courage and sacrifice: Surveys show that red is the colour most associated with courage – a symbol of martyrs and sacrifice, particularly because of its association with blood.Beginning in the Middle Ages, the Pope and Cardinals of the Roman Catholic Church wore red to symbolize the blood of Christ and the Christian martyrs. The banner of the Christian soldiers in the First Crusade was a red cross on a white field, the St. George’s Cross. In 1587, Mary, Queen of Scots, accused of treason against Queen Elizabeth I, wore a red shirt at her execution, to proclaim that she was an innocent martyr.

Courtly love, the red rose, and Saint Valentine’s Day:Red is the colour most commonly associated with love, followed at a great distance by pink.It the symbolic colour of the heart and the red rose, is closely associated with romantic love or courtly love and Saint Valentine’s Day. Both the Greeks and the Hebrews considered red a symbol of love as well as sacrifice. The Roman de la Rose, the Romance of the Rose, a thirteenth-century French poem, was the allegorical search by the author for a red rose in an enclosed garden, symbolizing the woman he loved, and was a description of love in all of its aspects.Later, in the 19th century, British and French authors described a specific language of flowers; giving a single red rose meant ‘I love you,’

Happiness, celebration and ceremony: Red is the colour most commonly associated with joy and well being. It is the colour of celebration and ceremony. A red carpet is often used to welcome distinguished guests. Red is also the traditional colour of seats in opera houses and theatres. Scarlet academic gowns are worn by new Doctors of Philosophy at degree ceremonies at Oxford University and other schools. It is the colour traditionally worn at Christmas by Santa Claus, because in the 4th century the historic Saint Nicholas was the Greek Christian Bishop of Myra, in modern-day Turkey, and bishops then dressed in red.

Dynamism, visibility, energy: Surveys show red is the colour most frequently associated with visibility, proximity, and extroverts. It is also the colour most associated with dynamism and activity.

• Red is used in modern fashion much as it was used in Medieval painting; to attract the eyes of the viewer to the person who is supposed to be the centre of attention. People wearing red seem to be closer than those dressed in other colours, even if they are actually the same distance away. Monarchs, wives of Presidential candidates and other celebrities often wear red to be visible from a distance in a crowd.
• It is also commonly worn by lifeguards and others whose job requires them to be easily found.
• Because red attracts attention, it is frequently used in advertising, though studies show that people are less likely to read something printed in red because they know it is advertising, and because it is more difficult visually to read than black and white text.

Hatred, anger, aggression, passion, heat and war: it also the colour most frequently associated with hatred, anger, aggression and war. People who are angry are said to “see red.” Red is the colour most commonly associated with passion and heat. In ancient times red was the colour of Mars, the god of War- the planet Mars was named for him because of its red colour.

Warning and danger: Red is the traditional colour of warning and danger. Several studies have indicated that red carries the strongest reaction of all the colours, with the level of reaction decreasing gradually with the colours orange, yellow, and white, respectively.

• Red is the international colour of stop signs and stop lights on highways and intersections. It was chosen partly because red is the brightest colour in daytime (next to orange), though it is less visible at twilight, when green is the most visible colour. Red also stands out more clearly against a cool natural backdrop of blue sky, green trees or grey buildings. But it was mostly chosen as the colour for stoplights and stop signs because of its universal association with danger and warning.
• In the Middle Ages, a red flag announced that the defenders of a town or castle would fight to defend it, and a red flag hoisted by a warship meant they would show no mercy to their enemy.
• In automobile races, the red flag is raised if there is danger to the drivers. In international football, a player who has made a serious violation of the rules is shown a red penalty card and ejected from the game.
• Red is generally used as the highest level of warning, such as threat level of terrorist attack in the United States.
• Teachers at a primary school in the UK have been told not to mark children’s work in red ink because it encourages a “negative approach”.

Seduction, sexuality and sin: Red by a large margin is the colour most commonly associated with seduction, sexuality, eroticism and immorality, possibly because of its close connection with passion and with danger.

• Red was associated with sexual passion, anger, sin, and the devil. Satan is often depicted as coloured red and/or wearing a red costume in both iconography and popular culture. By the 20th century, the devil in red had become a folk character in legends and stories. In 1915, Irving Berlin wrote a song, At the Devil’s Ball, and the devil in red appeared more often in cartoons and movies than in religious art. In the Old Testament of the Bible, the Book of Isaiah said: “Though your sins be as scarlet, they shall be white as snow.” In Roman Catholicism, red represents wrath, one of the Seven Deadly Sins.In both Christian and Hebrew tradition, red is also sometimes associated with murder or guilt, with “having blood on one’s hands”, or “being caught red-handed.”
• Adultery and prostitution:  In the New Testament, in the Book of Revelation, the Antichrist appears as a red monster, ridden by a woman dressed in scarlet, known as the Whore of Babylon:”So he carried me away in the spirit into the wilderness: and I saw a woman sit upon a scarlet coloured beast, full of names of blasphemy, having seven heads and ten horns. “And the woman was arrayed in purple and scarlet colour, and decked with gold and precious stones and pearls, having a golden cup in her hand full of abominations and filthiness of her fornication: “And upon her forehead was a name written a mystery: Babylon the Great, the Mother of Harlots and of all the abominations of the earth: And I saw the woman drunken with the blood of the saints, and with the blood of the martyrs of Jesus. In 17th century New England, red was associated with adultery. In the 1850 novel by Nathaniel Hawthorne, The Scarlet Letter, set in a Puritan New England community, a woman is punished for adultery with ostracism, her sin represented by a red letter ‘A’ sewn onto her clothes. Red is still commonly associated with prostitution. Prostitutes in many cities were required to wear red to announce their profession, and houses of prostitution displayed a red light. Beginning in the early 20th century, houses of prostitution were allowed only in certain specified neighbourhoods, which became known as red-light districts.