How do chromatophores work?

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Chromatophores are a type of cell (or group of cells) which are capable of reflecting light and which contain pigments.

The functioning of these cells vary from one organism to another. For example, cephalopods use multicellular "organs" to generate their quick color changes. Chromatophore units in these creatures consist of a chromatophore cell which holds a cytoelastic sacculus (a tiny sac of pigment granules) and many muscle, glial, nerve, and sheath cells. These tiny sacs of color are stretched when muscles controlled by the nervous system pull on them, expanding the sacs so that the color they contain can be seen. The color disappears when the muscles relax and the sacs shrink back to their normal size. 

In reptiles, amphibians, and fish, on the other hand, color shifts arise not out of a change in the shape of the color sac, but rather via the movement of pigment within the cell. 

The benefit of this kind of physiological color change lies in the ability to adapt to one's background; the camouflage provided by these cells helps organisms hide from perceived threats, as well as reflect different environmental and internal factors like mood, stress level, and temperature. 

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