“Coleoid cephalopods have complex multicellular organs which they use to change colour rapidly. This is most notable in brightly coloured squid, cuttlefish and octopuses. Each chromatophore unit is composed of a single chromatophore cell and numerous muscle, nerve, glial and sheath cells. Inside the chromatophore cell, pigment granules are enclosed in an elastic sac, called the cytoelastic sacculus. To change colour the animal distorts the sacculus form or size by muscular contraction, changing itstranslucency, reflectivity or opacity. This differs from the mechanism used in fish, amphibians and reptiles, in that the shape of the sacculus is being changed rather than a translocation of pigment vesicles within the cell. However a similar effect is achieved.
Octopuses can operate chromatophores in complex, wavelike chromatic displays, resulting in a variety of rapidly changing colour schemes. The nerves that operate the chromatophores are thought to be positioned in the brain in a pattern similar to that of the chromatophores they each control. This means the pattern of colour change matches the pattern of neuronal activation. This may explain why, as the neurons are activated one after another, the colour change occurs in waves. Like chameleons, cephalopods use physiological colour change for social interaction. They are also among the most skilled at background adaptation, having the ability to match both the colour and the texture of their local environment with remarkable accuracy.”