A very interesting video about cephalopod skin, with great images!
It also explains an experience designed to determine how much of the color changes is controlled by the brain or by the skin itself.
From the video:
While it’s still early to say, one possibility is that the skin itself is able to see and stimulate the chromatophores locally, bypassing the brain. A recent study at the Marine Biological Laboratory in Woods Hole, Mass., indicates that cuttlefish skin has light-sensing cells.