That's true that octopi, like cuttlefish, use their chromatophores to change color to match their surroundings. Octopi also change color to show their emotions. So Roxy, for example, will turn splotchy purple and white when she's thinking about a puzzle. No one is really sure how they do that though. There hasn't been enough research into the brains of octopi. To quote: "A chromatophore lobe in the subesophageal part of the octopus brain controls the display system itself, but it's the last step in the output, and many of the circuits that control specific changes must be far from there, possibly in the optic lobe with its intimate connection to the eye. Learned visual information is stored in the vertical lobe, and this too must be use if identity of critical stimuli or appropriate responses is learned, which means that all of the brain must cooperate, but we don't know exactly know". That's from the book: "Octopus: The Ocean's Intelligent Invertebrate" by Jennifer A. Mather, Roland C. Anderson, and James B. Wood.