Colour in the eye of the beholder : receptor sensitivities and neural circuits underlying colour opponency and colour perception
Colour vision — the ability to discriminate spectral differences irrespective of variations in intensity — has two basic requirements: (1) photoreceptors with different spectral sensitivities, and (2) neural comparison of signals from these photoreceptors. Major progress has been made understanding the evolution of the basic stages of colour vision–opsin pigments, screening pigments, and the first