How Octopuses Change Color

Octopuses are famous for their ability to change color in a fraction of a second. They use this skill to hide from predators, to surprise prey, and even to communicate with one another. The change is made possible by thousands of tiny structures in the skin called chromatophores. Each one is a small, elastic sac filled with red, yellow, brown, or black pigment and surrounded by muscles.

[A] Unlike most animals, which change color slowly through chemical signals, octopuses control their chromatophores directly with nerves. [B] When the muscles around a sac contract, they pull it open, and the color spreads over a wider area. [C] When the muscles relax, the sac shrinks back to a tiny dot that is almost invisible. [D] Other cells beneath the chromatophores reflect light, adding white, blue, and green tones.

One mystery remains. Most octopuses appear to be colorblind: their eyes contain only one type of light-sensitive cell, so they probably cannot tell colors apart. Yet they can match their surroundings remarkably well. Some researchers believe the answer may lie in the skin itself. In one species, scientists discovered light-sensitive proteins in the skin similar to those found in eyes, which may allow the skin to detect light directly.