Color and its change in fishes is a matter of colors already present being manifest, clumped or masked.
Of the most common types of chromatophores are melanophores. Thesecontain black or brown colored melanin crystals. The degree or intensity of darkness of these cells and hence the fish they’re found on depends on the amount of dispersion of the melanin pigment withinthe cell. Intracellular migration and aggregation is the fundamental chromatophores activity. When the pigment is dispersed widely throughout the cytoplasm, the skin macroscopically appears darker(black or brown). When the pigment granules aggregate or contract the cell loses its darkness.
Some examples of this loss of dark color are the dark bands on freshwater angels (Pterophyllum) andsunfishes (Lepomis) that can quickly blanch from dark to light or come back again given fright or excited states.
Other colored cell types include xanthophores and erythrophores. These chromatophores aregenerally slower to change. An example of these cells can be understood readily by looking at a swordtail (Xiphophorus).
Studies of skin pigment cells in recent years have helped our understanding ofpigment biology. Two important concepts have become established re the function of chromatophores re the dermal unit and the epidermal melanin unit. The epidermal unit is only concerned withmorphological color change (in warm and cold-blooded animals). The dermal chromatophores unit contains three layers:
The xanthophore or filtering layer
The iridophore or reflecting layer
The melanophore orabsorbing layer
Note that there are two types of pigments true or based on color and reflective. Also note that not all chromatophores contain the actual pigment color that they appear. That is, thatsome work on different principles other than selective absorption/reflection. The iridophores contain quanine crystals that reflect different wavelengths of light, which give them an apparent color...