 Each chromatophore contains pigment of only one colour . In fish and frogs , colour change is mediated by the type of chromatophores known as melanophores that contain dark pigment . A melanophore is star @-@ shaped ; it contains many small pigmented organelles which can be dispersed throughout the cell , or aggregated near its centre . When the pigmented organelles are dispersed , the cell makes a patch of the animal 's skin appear dark ; when they are aggregated , most of the cell , and the animal 's skin , appears light . In frogs , the change is controlled relatively slowly , mainly by hormones . In fish , the change is controlled by the brain , which sends signals directly to the chromatophores , as well as producing hormones . 
