any of a group of biological pigments (biochromes) conspicuous in the eyes of insects and crustaceans as well as in the changeable chromatophores (pigment-containing cells) in the skin of cephalopods. Although ommochromes, which are derived from the breakdown of the amino acid tryptophan, are responsible for the colours of insect eyes, they are not known to be involved directly in photoreception. In the changing integumentary cells of cephalopods, however, they may contribute to adaptive responses.