check out what it does around 3:30.
the cuttlefish (which is NOT a fish, or a vertebrate at all, in case you were wondering, but is closely related to squid and octopi) is interesting because it has such exquisite control over its pigmentation, such that it can change its patterning on the fly (as illustrated in the movie). each individual pigment cell has a cluster of muscle cells around it, controlling whether it is contracted (invisible) or extended (visible). pigment cells come in several colors, and by controlling each pixel at the cellular level, this amazing cephalopod is able to blend in with its environment, mimicking plants, other animals, and rocks as it chooses, or by parading around in threatening or seductive coloration it can warn off predators or attract a mate.
another interesting thing about cuttlefish is that although they can change colors, they cannot see colors, though they can detect the polarization of light. so somehow, though they do not have cone photoreceptors, they can match their own coloration to that of their environment.
read more about cuttlefish.