In nature, ‘colour’ is the manner in which our brains distinguish different wavelengths of light, perceived when they are emitted or reflected from an object or medium or a radiation source like the Sun or a burning flame. The longest wavelengths of light are perceived as red or orange, whilst intermediate wavelengths may be perceived as yellow or green, and short wavelengths are seen as blue or purple. But this is a rather simplistic view of the range of colours we see, as combinations of wavelengths in different proportions and intensities can create a vast range of detectable hues, shades and tones, some of which are identified as colours in their own right – turquoise, pink, mauve, brown, cream, magenta etc.
It is clear that any visible wavelength, or combination of wavelengths which we perceive can be described as colour. So how do black, white and grey measure up by this definition? First let us consider black.
Whether BLACK is a colour or not depends on our terms of reference. In terms of wavelengths of light, black is most definitely NOT a colour, because black, by definition, is the absence of any light. We see something as black, precisely because it is NOT emitting or reflecting any coloured light at all. As soon as light wavelengths of any colour are introduced, black ceases to exist.
On the other hand, black can undoubtedly be produced through manipulation of colour, in the form of pigments. Pigments are substances which absorb certain wavelengths of light while reflecting others. And if the right combination of pigments are combined together, then theoretically all wavelengths of light may be absorbed creating black. In such media as paint production and ink production, it is well known that this can be achieved by mixing together three different coloured pigments – namely Cyan, Magenta and Yellow (CMY*). Since black in this system is created by combining colours in the form of pigments, some would say that black itself could be considered a colour. However it can be countered that even though coloured pigments are used to produce black, it is only through the absorption of light by the pigments that this is achieved – ultimately, black is still being produced by an absence of coloured light).
On the other hand, however one describes black, WHITE most definitely IS a colour, because as we have seen, colour is not merely how we perceive individual light waves, but also how we perceive combinations of light waves. White is essentially how we visualise a combination of all wavelengths of light (or colour) at maximum intensity. This is illustrated above in the RGB system which uses Red, Green and Blue light to produce white. White could be described as the ultimate colour – the colour in which all other colours are combined together equally. The RGB system will be described in slightly more detail below.
(* In practice, the black produced by mixing together cyan, magenta and yellow is not perfect. It is also very expensive to combine inks in this way, so usually today a fourth black ink is added in printers – hence CMYK, in which the K refers to the black ink).