a rift

How octopuses distinguish colors (or do they?)

The question of how octopuses can match their surroundings while not being able to see colours is one hell of a puzzle. Christopher Stubbs may finally have found the answer: chromatic aberration.
Maybe octopuses do see colour – not from light hitting special retinal “photoreceptors” but thanks to chromatic aberration, where different colours of light focus at different distances behind a lens.
Eyes of cephalopods are quite unlike anything seen on land: U- and W-shaped pupils backed by a lens that moves back and forth, like a camera, rather than fattening or thinning like ours. But they also have only one photoreceptor, unlike our red, green and blue ones.
Stubbs idea is the following: by adjusting the focal point of their eyes, like a photographer adjusts a lens, cephalopods might be able to detect different wavelengths – or colours – of light. This is called chromatic aberration.
To test his idea, Stubbs created a computer model of how the animals’ eyes work and see if chromatic aberration was possible.
He found not only could a shifting lens do the trick, but the cephalopods’ quirky pupils only served to maximise the effect. As Stubbs says, these creatures might exploit a ubiquitous source of image degradation in animal eyes, turning a bug into a feature.
The unusual pupils of cephalopods (from the top, a cuttlefish, squid and octopus) allow light into the eye from many directions, which spreads out the colors and [certainly] allows the creatures to determine color, even though they are technically colorblind.
As the lens moved forwards and backwards, the different wavelengths focusing on the retina at different times built up a colour picture.
It is not a proof, but the idea is definitely worth investigating !
Text from this article. For more in-depth information, I suggest weird pupils let octopuses see their colorful gardens.