Evolution of human colour vision as 'visual purple' receptor proteins, are encoded by Rh1, OPN2 and RHO genes. They are characterized by extreme sensitivity to light and enable monochromatic human vision in low light or dim conditions. They are broken down into retinal and opsin when exposed to these conditions. Humans have 3 types of photopsin proteins found in the cone cells. Long Wavelength Sensitive Opsin (Red cone opsin) – Encoded by the OPN1LW gene with a λmax of 560 that is found in the yellow-green electromagnetic spectrum despite its name. Its sensitivity to the colour red is still known to be higher than the
Colour centre ventral occipital area plays an important role in colour vision. The search for the human equivalent of V4 led to the discovery of other areas that were stimulated by colour. The most significant was an area anterior in the ventral occipital lobe, subsequently named V4α. Further fMRI experiments found that V4α had a different function than V4, but worked cooperatively with it. V4α is involved in a number of processes, and is active during tasks requiring colour ordering, imagery, knowledge about colour, colour illusions, and object colour. The V4 and V4α areas are separate entities, but because of their close