It’s a Colorful Life

There’s a 90% or so chance that you’re something called a “trichromat.” The rest of you are almost certainly “dichromats.” It’s an easy thing to figure out, too. If you’re colorblind — and about 8% of men (and fewer than 1% of women) are — you’re the latter. Just about everyone else is a trichromat. Dichromats often struggle to determine the difference between red and green while trichromats can differentiate between about a million different hues.

And then there’s the occasional tetrachromat — a person with especially powerful eyes which may be able to differentiate between 100 million colors. Maybe.

Whichever camp you belong to, your eyes work in relatively the same way. We all have something calls rods and cones, which together are the photoreceptors in our eyes. The cones are the parts which, with sufficient light, detect color. Most of us — the trichromats — have red, green, and blue cones. (That’s where the “tri-” part of the word comes from; it’s a reference to the three types of cones.) Dichromatic people have a slight genetic mutation which causes only two of the three cones to be present. Those people can’t easily detect colors involving the missing cone, which is why they’re typically referred to as “color-blind.”

But there’s another mutation — one which has the opposite effect. Instead of having two or three cones, these people are tetrachromatic — they have four cones. The mutation itself isn’t all that rare; according to the Post-Gazette, around 12% of women likely have four cones. The fourth cone, though, doesn’t do much at all for most of them. In many cases, the cone detects light from wavelengths which are very close to the wavelengths detected by the three typically-occurring cones cones (e.g. the fourth cone could detect a range of reddish-oranges), leading to no appreciable difference in that person’s ability to detect color. But in theory, some people should have a fourth cone which is significantly different than the other three, and those people should be able to see a wide world of color unknown to the rest of us. Per some estimates (cited in the above-linked article), 2.5% of or so of women may have the right type of extra cones — enabling them to see millions of colors more than the rest of us mere mortals.

The ability isn’t very easy to detect, though, so we’re really not sure. In 2012, Gabriele Jordan, a neuroscientist at Newcastle University, announced that she had successfully identified someone who could see these extra 99 million colors, the first time this had happened. Dr. Jordan’s test focused on 25 women who, genetically, were determined to have four cone sets, and, according to Digital Journal, were then asked to answer questions “designed to detect an extended range of color vision.” Twenty-four of the women failed, despite their extra cones. But one subject, known only as cDa29, passed. Dr. Jordan and others believe that there are many more women out there with this unusual ability.

Even then, though, there are a few reasons to believe that the ability doesn’t lend itself to any specific superpowers. It’s unclear how our brains would deal with the extra color information even if we had access to it — it’s very possible that cDa29 is an enormous outlier. And even then, with the vast majority of the world only having three sets of cones, who knows if there’s anything a tetrachromatic can do to explain her experience to others. After all, how does one describe “red” to someone who is colorblind? The same problem holds for tetrachromats who want to explain what they’re seeing to the rest of us.

Bonus Fact: Butterflies have five cones — they can see a much wider range of color than even the tetrachromats among us. But that’s pedestrian compared to the mantis shrimp, which has as many as sixteen. This comic by The Oatmeal (whose site contains some R-rated language and imagery) goes into more detail.

From the ArchivesThe Case of the Missing Magenta: Why we can see pink, even though it doesn’t exist as a wavelength.

RelatedColorblindness test books, to determine if one is colorblind.