A chromatophore are specialized cells which can contain or produce pigment, or reflect light in a specific way to create a certain desired hue. They are found in cold blooded animals like fish, amphibians, reptiles, crustaceans, and cephalopods, along with certain bacteria. Chromatophores serve a number of functions; in addition to coloring the skin and eyes of these animals, the cells can also help to protect the animals from predators or radiation, and they are used to signal other creatures. Scientists also use chromatophores to study various aspects of animal life; the cells have been identified and studied since the early 1800s.
Some biologists break chromatophores up into two rough categories: biochromes and schemochromes. Biochromes actually contain and produce pigment, while schemochromes can change the way that light reflects from the skin of the animal, thereby changing its color. Biologists may also classify a chromatophore by the colors that it produces; cyanophores, for example, produce colors in the blue range. Iridescent animal coloring is produced by iridophores.
In addition to simply creating flat color, many chromatophores can also be used to help an animal change color. This trait is often observed in animals like octopi, lizards, and some fish. The cells can accomplish a color change by expanding or contracting each individual chromatophore to cover varying areas of the animal's skin, in response to stimuli like light. In addition to making excellent camouflage, these color changing cells can also help an animal regulate its body temperature, or they can signal information to other animals of the same species.
People who have observed the rapid color change of animals like octopi have probably noticed that the color change spreads like a blush, rather than happening all at once. This appears to be caused by a sequential firing order for neurons in the brain as they respond to a changing environment. Creatures like octopi with a highly refined chromatophore control system can mimic the color and texture of their environment remarkably well; this camouflage technique is used to hide from predators and also to pursue unsuspecting prey.
Photosynthetic bacteria also use chromatophores, to help them produce energy. The pigments in bacteria may take the form of bacteriochlorophyll, and they are capable of photosynthesis. Different bacteria may use and arrange their chromatophores in different ways, depending on how they evolved and where they live. Depending on the bacteria, the colors a chromatophore takes can range from rich brown to bright green.