The cuttlefish wears its nervous system on the outside. Beneath its skin lie millions of chromatophores—tiny sacs of pigment, each ringed by muscles the animal can flex at will. Contract the muscles, and a sac stretches into a visible disk of color; relax them, and the color shrinks to a pinprick. Because the cuttlefish controls each sac directly, it can repaint its entire body in a third of a second, sending ripples of stripe and blush across its flanks. What makes this feat stranger still is that cuttlefish are, by every test biologists have devised, colorblind. They possess a single type of light receptor, incapable of distinguishing wavelengths the way our three types do. And yet they match the hues of coral, sand, and weed with uncanny precision. How? One leading hypothesis points to the shape of their pupils, which may smear incoming light into its component colors, letting the animal read color from blur rather than from pigment—a workaround as elegant as it is bizarre. If the idea holds, the cuttlefish sees color not with special cells but with a trick of optics, painting a world it cannot, in the ordinary sense, perceive.