Abstract
The theory of trichromatic human colour vision was proposed over 200 years ago and the existence of three types of cone photoreceptors was confirmed in the 1980s. I will summarise current views of how the signals from cone photoreceptors are organised into “blue-yellow” and “red-green” pathways in the subcortical visual system. These pathways can be distinguished at the first synapse in the visual pathway, between cone photoreceptors and cone-contacting bipolar cells, and remain segregated in the subcortical afferent visual pathway. I will review evidence from molecular biology, anatomy, and physiology showing that the blue-yellow pathway likely forms a primordial colour vision system common to most diurnal mammals, whereas the red-green pathway is unique to primates and evolved together with high-acuity spatial vision.