Tiny muscle-controlled color sacs called chromatophores expand and shrink to change the octopus's skin color.

The top layer of octopus skin has millions of these tiny sacs. Each sac is like a tiny water balloon filled with paint. Special muscles pull the balloon wide to show the color, or let it shrink to a tiny dot to hide it. These sacs come in yellow, red, and brown. By mixing them, the octopus creates different patterns.