Cuttlefish can't see color, yet they camouflage to match their surroundings' colors

Cuttlefish have only a single type of photoreceptor, which should make true color vision impossible, yet they produce some of the most precise color-matching camouflage in nature using skin cells called chromatophores. Researchers suspect they may sense color indirectly through light-sensitive skin, or by using their oddly shaped W-pupil to split light by wavelength, a puzzle still not fully resolved.

— Roger Hanlon and colleagues (research literature), Cuttlefish camouflage and vision — Marine Biological Laboratory research summarized by the Royal Society