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Chameleons of the ocean, cephalopods are able to change not only the colour, but also the texture of their skin resembling their environment or to communicate. These pictures show only a fragment of the abilities of the cuttlefish. See also the cuttlefish article and the video.
Flamboyant Behaviour
Flamboyant behaviour is used to deter or distract predators. Also used to confront a competitor during mating or protection of territory.
General background resemblance
Have another look.....One of the primary defense mechanism of a cuttlefish is to blend in with the background (crypsis) not only taking on the colour of the substrate, but also the structure.
General background resemblance

On a different substrate you need different colours. This greyish, mottled pattern resembles the sandy substrate quite all right.