How ‘colorblind’ cuttlefish may see in living color

Animals like cuttlefish and octopuses can rapidly change color to blend into the background and dazzle prospective mates. But there’s only one problem: As far as we know, they can’t see in color. Unlike our eyes, the eyes of cephalopods—cuttlefish, octopuses, and their relatives—contain just one kind of color-sensitive protein, apparently restricting them to a black and white view of the world. But a new study shows how they might make do. By rapidly focusing their eyes at different depths, cephalopods could be taking advantage of a lensing property called “chromatic blur.” Each color of light has a different wavelength—and because lenses bend some wavelengths more than others, one color of light shining through a lens can be in focus while another is still blurry. So with the right kind of eye, a quick sweep of focus would let the viewer figure out the actual color of an object based on when it blurs. The off-center pupils of many cephalopods—including the w-shaped pupils of cuttlefish (above)—make this blurring effect more extreme, according to a study published this week in the Proceedings of the National Academy of Sciences. In that study, scientists built a computer model of an octopus eye and showed that—for an object at least one body length away—it could determine the object’s color just by changing focus. Because this is all still theoretical, the next step is testing whether live cephalopods actually see color this way—and whether any other “colorblind” animals might, too.