Well, I was watching a video about chameleons and I saw that their cells can change color. Can someone explain me how is this possible?
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When it comes to displaying color, most organisms use chromatophores. Chromatophores are pigment-containing and light-reflecting cells, or groups of cells. Chromatophores reflect the color that they look like.
Chameleons also use chromatophores. The outermost layer of the chameleon’s skin is transparent. Beneath this layer are the chromatophores. The deepest layer contains melanophores, which are filled with melanin. Above that layer are cells called iridophores, which have a blue pigment that reflects blue and white light. Layered on top of those cells are the xanthophores and erythrophores, which contain yellow and red pigments, respectively.
For a chameleon to change color, it must expand or contract certain chromatophores depending on the signal of the nervous system. The expanded chromatophores block the contracted ones and the color of the expanded chromatophores determine the color of the chameleon. For example, to make the chameleon green, the iridophores and xanthophores must expand, and melanophores and and erythrophores contract.
WIRED - How Chameleons Change Colors
More to read This Nature article provides a detail description and explanation of how this occurs - Photonic crystals cause active colour change in chameleons