“Cephalopods are among nature’s most colorful animals. Not even a chameleion . . . can compare with octopuses and squids when it comes to the variety and speed of color-changing wizardry. Cephalopods are unique in nature for in no other animals are color changes brought about by muscular control.

The strange, beautiful, and often startling color effects are the work of tiny pigment or color cells known as chromatophores which are located just beneath the skin. . . .

Among cephalopods the usual pigments are black, brown, red, yellow, and orange-red, and also many variations of those colors. No cephalod, however, has chromatophores with all these colors. Three pigments are the usual number in one animal.

The size of the chromatophores can be changed at will by the animals, as each cell is an elastic sac. Around it, radiating outward like spokes in a wheel, are microscopic strands of muscle. When these tiny muscles are relaxed there is no tension in the color sac and it remains small, so small that its pigment does not show. But when the muscles contract, they pull the chromatophore’s wall outward in all directions, making it much larger. Now its color pigment shows.

There are many thousands of these color bodies in the octopus’s skin and if they all happened to contract the creature would be a white or white-gray. When his chromatophores expand he takes on the color of their pigment and the change may take place as you watch. Many times you can actually see color ripple over his body.”

—Joseph J. Cook & William L. Wisner, The Phantom World of the Octopus and Squid, 1965.