Key Questions in Design
- Does ‘colour’ exist?
- Why is colour so difficult to define?
- Why is mixing and combining colours so unpredictable?
Colour is the range of wavelengths
of the electromagnetic spectrum
that are visible to the human eye.
Physical properties of light
Light consists of waves of electromagnetic energy which travel at different wavelengths.
Colour is the range of wavelengths of the electromagnetic spectrum that are visible to the human eye. Many other animals can perceive more wavelengths than we can.
When light strikes a surface, certain wavelengths are absorbed and others are reflected by its pigments or colouring matter. This process gives the object its surface colour. Naturally occurring colours are not just light at one wavelength, but actually contain a whole range of wavelengths across the whole light spectrum.
Different combinations of reflected wavelengths form all the observed colours.
Although pure white light is perceived as colourless, it actually contains all colours in the visible spectrum. When white light hits an object, it selectively blocks some colours and reflects others; only the reflected colours contribute to the viewer’s perception of colour.
A colour’s “hue” describes which wavelength appears to be most dominant. The object whose spectrum is shown below would likely be perceived as bluish, even though it contains wavelengths throughout the spectrum.
Although this spectrum’s maximum happens to occur in the same region as the object’s hue, it is not a requirement. If this object instead had separate and pronounced peaks in just the the red and green regions, then its hue would instead be yellow (see the additive colour mixing table).
Although the spectrum of lightwaves exists along a continuum, there are peaks of sensitivity or human perception that appear to be ‘hardwired in’ but also individually and culturally variable. In many cultures we distinguish separate bands of wavelengths. (is this universal?? eg some do not distinguish green and blue)
Optical colour: additive and subtractive processes
Wavelengths reaching our eye – optical colour – are a combination of:
- Surface or local colour
- Lighting conditions
Virtually all our visible colours can be produced by utilizing some combination of the three primary colours, either by additive or subtractive processes.
Subtractive processes are more susceptible to changes in ambient light, because this light is what becomes selectively blocked to produce all their colours. This is why printed color processes require a specific type of ambient lighting in order to accurately depict colours.
Colour properties: Hue, Value and Saturation
A colour can be defined in terms of its hue, its brilliance and its saturation. Visually describing a colour based on each of these terms can be highly subjective, however each can be more objectively illustrated by inspecting the light’s colour spectrum.
Hue
Hue is the position of a colour on the colour spectrum (see above). A colour’s “hue” describes which wavelength appears to be most dominant. Naturally occurring colours are not just light at one wavelength, but actually contain a whole range of wavelengths (see pigments below).
Hues are conventionally represented in colour wheels that can be used to help mix and also combine colours.
Value/tone
The brain responds first to tonal and value structure of an image because the simple light/dark signals passed by the rods reach the brain more quickly than colour from the cones.
The actual range of lightness and darkness differs between hues, and this can cause difficulties in matching the brilliance. Yellow can only vary between a medium tone and very light; there is no such thing as a dark pure yellow. Red becomes pink when very light, and so loses its main qualities. Blue, however, covers the full range.
Saturation
Saturation is a variation in the purity of a colour. A highly saturated colour will contain a very narrow set of wavelengths and appear much more pronounced than a similar, but less saturated colour. As they become less saturated, they become more grey, less ‘colourful’, and dirtier. Colours become unsaturated when they are mixed with white, black, grey or their opposite colours on the colour circle. Including saturation
