– Colour is what enables two objects of identical shape and structure to be differentiated, for example the French and Italian flags.
– Colour is what is neither grey, nor white nor black (black and white are the extremes of the neutral grey scale)
– Colour is the sensation produced by physically defined radiation (called stimulus), which enters the eye and is captured by millions of cones on the retina but which is especially concentrated in the central part called the fovea, which is the centre of the sharpest vision .
– Colour is sometimes used to denote a substance ("Eat your greens").
– Colour is sometimes confused with tonality. For example within a green tone, there are more or less light or dark greens. A colour is unique.
– There are two trichromatic systems (three primary colours) by additive synthesis where the primary colours are Red-orange, Green, Blue-violet (RGB) and subtractive synthesis where the primaries are Cyan, Magenta, Yellow (CMY).