Primary colour
One of a small set of colours from which a wide range of others can be mixed.
Also: primaries
Primaries are the starting colours of a mixing system. There is more than one set. For light, as on screens, the primaries are red, green and blue. For printing inks they are cyan, magenta and yellow. Art classes traditionally teach red, yellow and blue, which work fairly well with paints but cannot mix every colour. No set of three real primaries can produce all the colours the eye can see. The idea of three comes from human vision, which has three kinds of colour-sensing cell.