Having multiple types of visual pigments inside the cones allows animals to see in colour because these pigments are sensitive to different wavelengths of light. (nhm.ac.uk)
The team discovered that visual pigment genes have changed substantially during snake evolution, including many changes to the wavelengths of light that the pigments are sensitive to. (nhm.ac.uk)
The researchers speculated that mammalian melanopsins have acquired different molecular properties from closely related invertebrate visual pigments in order to function in the non-visual photoreception. (sciencedaily.com)