Octopuses are technically colourblind — their eyes only have one type of light-sensing cell — and yet they can match the colour beneath them in under a second, which researchers think is because th...

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Roger Hanlon has spent decades studying cephalopod camouflage at the Marine Biological Laboratory in Woods Hole, and he still sounds a little amazed by how fast it happens. Asked once how quickly an octopus can change its skin pattern, his answer was immediate: “Oh, the fastest ever. We’re talking as fast as 200 milliseconds — that’s one fifth of one second, the fastest human eye blink you can do.”

That single number is the mystery in miniature, because the animal doing it is, by most conventional definitions, colorblind.

What does “colorblind” actually mean for an octopus?

Color vision in most animals depends on having more than one type of photoreceptor, each tuned to a different wavelength of light, so the brain can compare their signals and extract color.

Cephalopod eyes generally have just one photoreceptor type, which is the biological definition of colorblindness. Alexander Stubbs, a graduate researcher at UC Berkeley who co-authored a 2016 study on the question, put the puzzle plainly to Berkeley News: “We believe we have found an elegant mechanism that could allow these cephalopods to determine the color of their surroundings, despite having a single visual pigment in their retina.”