How Does the Eye See Colour?

Human colour vision relies on three types of cone photoreceptor cells in the retina, each containing a different light-sensitive pigment (opsin) tuned to a different wavelength range: short (blue, ~420 nm), medium (green, ~530 nm), and long (red, ~560 nm). When light enters the eye, it stimulates these cones in varying proportions depending on its wavelength. The brain interprets the ratio of signals from the three cone types to produce the perception of a specific colour. This trichromatic system allows us to distinguish roughly 10 million colours. Rod cells, a separate type of photoreceptor, handle low-light vision but do not detect colour — which is why everything looks grey in dim light.