Even though octopuses belong to a group of shellfish called mollusks, they have no outside shell. A tough skin, called a mantle, covers the octopus’ body. This mantle contains small bags of pigment, or coloring matter, which are connected to the animal’s nervous system.
Any outside stimulus that excites the octopus makes its skin change color. It can change to blue, purple, brown, red, gray, white, and sometimes even striped.