I got frustrated with Snopes last night because they posted an article validating some of the untrue things people (including people who should know better) claim about color vision. Specifically they said dogs see things only in shades of blue and yellow. Here's the real deal.
Dogs have two color receptors in their eyes, they're named the blue cone and the yellow cone after the color of light they're most sensitive to. But both are actually sensitive to a whole swath of colors. I don't have an image for cone light sensitivity dogs but here's one for humans (thanks to Wikipedia). Dogs have one less set of cones than (most) humans but it's a similar deal.
You can see cones don't just pick up one color, they pick up a big swath of colors of light and our brains compare how much light the different cones sense to extrapolate what color an object is.
Dogs' "yellow" cones are actually quite close to our "red" cones and also our "green" cones. Our "red" and "green" cones are extremely close in form and what they see. The cone names are just convenient names. "Red" cones in humans are named for the longest wavelength they can see and "yellow" cones in dogs are named after what light they're most sensitive to. It would be just as accurate to call human "red" cones "yellow-green" or "yellow".
Given how much confusion it's caused we probably shouldn't have named the cones after specific colors. Some researchers refer to the cones as S, M, and L cones instead of blue, green, and red cones. That's short for short, medium, and long after the relative wavelengths of light they pick up. That should be adopted more broadly.
Despite the names of their cones dogs don't just see in shades of blue and yellow, they can see red (but not as far down the spectrum as us) and up into the ultraviolet a bit. They have less ability to discern colors than humans but do still see them.
If you think about it you don't see the world in shades of blue, green, and yellow-green despite those being the peak sensitivities of our cones. And that's because those cones are pretty broad and overlap a lot. Some wavelengths of light are sensed by all three cones.
Not coincidentally that place the cones overlap is at the peak intensity of sunlight, right where the blue and green portions of the spectrum meet. It makes sense to concentrate your ability to discern color where you'll have the most light available to do it with.
The reason this whole misconception drives me crazy is I am colorblind, which means in my case, like a dog, I only have two kinds of cone. The genes for one of my "red" or "green" cones mutated so it's sensitive to the same frequency as the other (I think they're both "red" but I'm not sure).
Human "red" and "green" cones are extremely close together as you can see in the picture below (it's the same one as above) they almost match up compared to "blue". That means that those two are to some extent duplicating each other so my color vision is much much closer to normal than if I'd lost the blue cone.
So I miss a solid chunk of color but for the most part I can see enough to get along on my vision plus some context. It often is challenging to realize someone is colorblind, people unconsciously compensate for it. Often colorblind people don't realize they're colorblind themselves.
People like me are called "red-green" colorblind after the name of the receptors that have an issue in our eyes, not after the name of colors we get confused. That can vary from person to person but red and green being confused is rarely the biggest problem. Some combination of green, yellow, orange, orange, and red, or purple and blue tend to be where people struggle. I sometimes have a much harder time with browns and reds, greens, or oranges of a similar shade than most people do.
It's a bit difficult to test exactly whats wrong for an individual so everyone with problems with red or green receptors gets the red-green label. We don't all see the same, but our problems are pretty similar. Sometimes green is moved and sometimes red. Sometimes they're the same and sometimes they're just closer than they should be.
There are other kinds of colorblindness that come from loss or alteration of blue cones or two or more cones. Some of those people have monochromatic vision and some of them are much more limited in color vision than red-green colorblindness.
Colorblindness affects you more in dim light. Some of what three cones do is allow you to keep making fine color distinctions as you have less light to work with. Color vision is different for different people. That's true of people who aren't colorblind as well, not everyone has exactly the same properties in their cones (or their brains). The difference is in whether you can gather enough information to distinguish everything.
Colorblindness is more common in men than in women but isn't considered rare in either. Extremely rarely someone will have 4 different cones and see more color than normal, they think that is more common in women or only occurs in them but there's so few verified cases it's hard to be sure.
People (and animals) with four cones are called tetrachromats, people with three are trichromats, people with two are dichromats, and people with one are called monochromats. Humans are mostly trichromats with quite a few dichromats thrown in a few monochromats and probably a handful of tetrachromats.
But sometimes just focusing on the number of color sensors is deceptive. Because two of our cones are so similar normal humans have much less ability to discern colors than you might expect from a trichromat. When humans engineer cameras we space the sensitivities of the red green and blue pixels out more evenly giving them a lot more ability to resolve color. It helps with engineering displays too, it's easier to simulate color using a combination of three colors than it would be if our cones had better spacing.
Anyways, thank you for reading my spontaneous color vision essay. Even if you hear it on a lot of popular science things, dogs can in fact see a fair bit of color and dogs can look up. And so can I.
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