The three types of cones are commonly most sensitive to three different colours (blue, green and red) due to

Retinal is the light-absorbing part of all visual photopigments. In the human retina, there are four different opsins, three in the conesand one in the rods. Small variations in the amino acid sequences of the different opsins permit the rods and cones to absorb different colours (wavelengths) of incoming light.

Colour vision results from different colours of light selectively activating the different cone photopigments. The sensations of different colours are produced by various combinations of these cones and their photopigments. When these cones are stimulated equally, a sensation of white light is produced.