Photo: Nemo's great uncle (flickr)
Clever cephalopods and colorblind camouflage champions—cuttlefish!
Cuttlefish are cephalopods, relatives of squid and octopuses, and are masters of camouflage. Using unique skin pigment cells, cuttlefish can rapidly change their skin color and pattern to blend in with the background. Amazingly, they do this despite being totally colorblind! Color-sensing cells in the retinas of cuttlefish eyes are composed of only one type of cone cell. Humans have three different types, each sensitive to a different color of light. With only one cone type, you couldn’t differentiate between different colors.
Using night-vision video, scientists at Woods Hole Marine Lab also discovered that cuttlefish even match their background at night, when there isn’t enough light for color vision. This suggests that it isn’t necessary for the cuttlefish to see colors in order to match them.
They also put cuttlefish in tanks with a range of different checkerboard patterns to see how well they could differentiate between different colors or brightness. When in front of a high-contrast background, like alternating dark and light squares, the cuttlefish skillfully mimicked the checkered pattern. They also tried checkerboards of different colors that were very similar in brightness. That is, colors that would look the same shade of grey in a black and white photo. In front of these low-contrast checkerboards, the cuttlefish just turned a single solid color.
So it seems that cuttlefish camouflage themselves by matching light intensities of objects rather than their colors. But how they match colors so accurately is still a mystery.