Question: what colour do cats see

Jo Brodie answered on 7 Mar 2021:

Cats can probably see a range of mostly greens and blues, as well as greys. They can’t see as many colours as humans can, but their vision at night-time is much better than ours.
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Both your eyes and a cat’s eyes have ROD and CONE cells in the retina (the ‘seeing’ bit of each eye) which detect light. The cone cells come in different varieties and each type detects a slightly different band of colour, and our cones (and our brains) work together to show us all the colours of the rainbow. Cats’ eyes don’t have as many cone cells as we do and their cones don’t have as much variety, so their colour vision is more limited than ours. Rod cells don’t detect colour but are very sensitive at low light levels. Cats’ eyes have lots of rod cells so they can see well when it’s dark and they can pick out more shades of grey.
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There are several ways of finding out what a cat or human eye can *detect* (what sort of light the eyes can pick up) and what the cat or human can *see* (which is what happens when our brain interprets that information). But first, have a look at the Checker Shadow optical illusion https://upload.wikimedia.org/wikipedia/commons/b/be/Checker_shadow_illusion.svg. The squares marked A and B are exactly the same shade of grey. Even though I know [1] this the two squares still look very different to me. Our eyes can see two things of the same shade or colour but, depending on the context, our brains might interpret them as being different.
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Eye doctors can measure how our eyes’ (and cats’ eyes if you can get the cats to sit still for long enough) respond to different flashes of light on the retina. From this (and other studies) we know that cats’ eyes are most sensitive to shades of blue and to shades of green (quite a yellow-green, but we don’t know if they can see what we’d call yellow).
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Another way to test this is for scientists to train a cat (good luck!) to pick the “odd colour out” and give it a food reward every time it gets it right (you can try a version for people here https://en.vonvon.me/quiz/1121#question [2]). This really only tells us that the cat can see a difference between the colours, not *how* it sees them or what colour it thinks it’s looking at. That we just can’t know.
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Jo
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[1] Checker Shadow Illusion – there are suggestions for how to prove to yourself here that the squares are the same colour; a bit of paper with holes cut out to match is one way https://en.wikipedia.org/wiki/Checker_shadow_illusion#Verification
– for a more colourful optical illusion, have a look at ‘The Dress’ https://www.romanoriginals.co.uk/thedress
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[2] Odd colour out – there’s an even harder version here https://www.buzzfeed.com/jamiejones/can-you-spot-the-odd-colour