Anatomy
Colour Vision
Our ability to discriminate colour is due to the varying sensitivities of three types of cones. They are named blue, green and red for the colour they absorb most strongly.
The three types of cones are named for the colour they absorb most strongly (blue, green, or red).
The three types of cones have broad and somewhat overlapping sensitivities. Light of a particular colour wavelength (energy level) may be absorbed by one or more cone types (blue, green and/or red).
When that happens, the relative intensity of stimulation of the one or more cone types is compared in the brain. As a result, the light is interpreted as a single intermediate colour, rather than as light composed of two distinct colours.
Read MoreIn fact, if one spot on the retina is simultaneously illuminated with two distinct colours, the brain will "see" the corresponding intermediate colour.
For instance, simultaneous illumination of the retina with red and green light causes us to see yellow, even though no light of the yellow wavelength is present. Simultaneous illumination with red, green, and blue light (equal stimulation of all three cone types), causes us to see white. Exactly what happens in the brain during the process of colour perception is still unknown.