Colour vision is the perception of different wavelengths of visible light (400 to 750 nm; VIBGYOR) as distinct colours, mediated by the three types of retinal cones.
Colour has three characteristics: hue, saturation and intensity.
Characteristics and Basis of Colour Vision
Three primary colours — red, green and blue — mixed in varying proportions produce any colour; equal proportions produce white.
Cones are the receptors for colour vision; the colour perceived depends on the type, number and pattern of cone stimulation.
Each colour has a complementary colour (e.g. purple-green, orange-blue, yellow-dark blue); mixing a colour with its complementary colour produces white.
Purkinje shift: spectrum's brightest part is green in dim light (scotopic, rod-mediated) and yellow in bright light (photopic, cone-mediated).
Colour perceived also depends on background colour (e.g. green letters invisible against a green background) and on light intensity, which changes the perceived shade.