What do we know about the physiology of colour vision? Which aspects of the colour vision can trichromacy explain and which is it unable to explain?

Colour vision is the ability of an organism or machine to distinguish components of the environment based on the reflection, omission or transmission of wavelengths. A human's perception of colour is a subjective process whereby the brain responds to the stimuli that are produced when incoming light reacts with the several types of cone photoreceptors in the eye. In essence different people may see one subject in different ways. The trichromatic theory of colour vision constitutes one mechanism by which the perception of colour may be achieved. The theory was proposed by Young in 1802, based on a colour matching experiment in which participants had to match an arbitrary colour by mixing wavelengths of three lamps. The test lights were always primary colours. The target light was an arbitrary colour. Findings highlighted that the target light could only be achieved by mixing all three of the test lights. By mixing less than all 3, the target could not be achieved but by mixing 4 colours, uniqueness disappeared in that different matches could achieve same colour! From this, Young inferred that colour perception depends on three different types of cone receptors within the eye. Hermann von Helmholtz developed the theory further in 1850, and highlighted that the three types of cone photoreceptors could be classified as short-wavelength (S cones), middle-wavelength (M cones), and long-preferring (L cones). Trichromatic theory of colour vision proposes that colour is encoded by the ratio of firing patterns across the three cone receptor types, where S cones respond most strongly to short wavelength, M cones to medium wavelengths and so forth. In this essay the trichromatic theory of colour vision will be reviewed and