Melanin

Dark biological pigment (biochrome) that produces buff, red-brown, brown, and black colors. Melanin occur widely in the feathers of birds; in hair, eyes, and skin of mammals, including humans; in skin or scales of many fishes, amphibians, and reptiles; in the ink of cephalopods (octopus, squid); and in various tissues of many invertebrates. Melanin protects the skin from ultraviolet radiation, and an increase in melanin is responsible for the so-called tanning of human skin exposed to sunlight. It is used as a colorant, particularly as it occurs in cuttlefish ink.