An octopus can change the color of its skin to blend in with its surroundings. How octopuses match their skin color to their surroundings is still an unsolved mystery. The pieces that scientists do understand begin in the skin, so that is where the evidence for how the skin works begins. An octopus's skin has special pigment cells called chromatophores that let it change color. Its skin has three layers of chromatophores, and the pigment in each layer reflects a different color. Tiny muscles around each color sac squeeze it open or let it close, so the color shows more or less, and octopuses can change color faster than almost any other animal.

Pigment is only part of the picture. Iridophores are skin cells that make shiny, rainbow-like colors. They contain a protein called reflectin that stacks up inside the cells and works like a mirror. Leucophores are skin cells with white pigment that scatter light and help control the contrast and brightness of colors. Pigment cells, mirror cells and white cells are all part of one skin. These kinds of cells can work together, as the blue-ringed octopus shows. Blue-ringed octopuses use their chromatophores and iridophores to make the iridescent blue rings appear when they are alarmed. The rings are an example of aposematism, bright colors used as a warning.

Octopuses have no hard shell or outside armor, so they had to evolve ways of not being seen. An octopus also has a soft body with no bones. The mimic octopus takes the idea of disguise a step further than simply blending in with the background. Fishermen in Indonesia first detected the mimic octopus in 1998. It can copy the look and moves of several different animals, and its choices are not random, because the mimic octopus takes the form of a sea snake only when it is bothered by damselfish, which sea snakes prey on. As of November 2026, it can successfully impersonate at least 16 very different animals, according to Guinness World Records.

Now the mystery itself. You may have heard that octopuses change color because they see the colors around them and copy them. In fact, most octopuses are technically color-blind, yet they can still match the colors around them. An octopus eye is built much like a human eye, but octopus eyes have only one type of photoreceptor, which means they can detect differences in brightness but not color in the usual way. So the eyes alone cannot explain how the skin gets its colors right, and that leaves scientists with a genuine question about the whole system. How octopuses match their skin color to their surroundings is still an unsolved mystery.

Words to know

• iridophores: shiny cells
• reflectin: mirror protein
• leucophores: white cells
• aposematism: warning colors
• photoreceptor: light-sensing cell