MODEL RELEASED. Colour vision. Conceptual image of red, green and blue light shining on a woman's eye. Human colour vision arises due to structures called cone cells on the retina, a light-sensitive membrane in the eyes. There are three types of cone cell, and together they detect the part of the spectrum known as visible light, but are most sensitive to the parts of the spectrum known as red, blue and green light respectively. It is the combination of the three signals from the three types of cone cells, that allows a varied range of colours to be perceived by the human brain as it processes signals from the eye. This is known as trichromacy, or three-colour vision.