A compound that gives colour to a tissue. Pigments perform a variety of functions. For example, haemoglobin in vertebrate erythrocytes gives blood its characteristic red colour and enables the transport of oxygen throughout the body (see respiratory pigment). Other biological pigments include chlorophyll, a photosynthetic pigment in plants that is responsible for their green coloration; and melanin, a brown pigment in animals that provides protection from ultraviolet light and can be used in camouflaging colorations. See also rhodopsin.