Physics and biology of colour and vision

The essential notions of the physics and biology colours are presented, starting with the rainbow, a phenomenon studied by Newton. Colours are properties associated to the larger or smaller deviation of light caused by a glass prism which correspond to different light wavelengths. The white light emitted by the sun includes all colours, while a laser light is monochromatic. There is invisible light of various types, i. e., light which do not correspond to colours: their wavelengths are smaller than that of the violet and larger than that of the red. In view of our evolutionary history in a planet near the sun, a star which mainly emits visible light, we see only this kind of light. Our identification of colours takes place in the retina in threekinds of receptors called cones, associated with the capture of red, green and blue light. Primates see, in general, in a way similar to humans, but there is a range of animal species whose vision is not trichromatic: this range goes from monochromatic whales to the extreme multichchromatism, due to 16 types of cones, of stomatopods, which are marine crustaceans. As the genes encode the cones of each species, one current area of research is the disentanglement of the genetic history which enabled vision enhancement in some animals and not in others. Darwin's theory is at work: the adaptation to tehenviroment was instrumental in the process that led to teh development of vision in animals