Tetrachromacy

What is tetrachromacy?

Tetrachromacy is a rare ability that gives people assigned female at birth (AFAB) extraordinarily sensitive color vision. People with tetrachromacy have four types of cones and can tell apart hundreds of millions of colors. Cones are a type of photoreceptor, light-detecting cells in your retinas. Most people have three types of cones and can tell apart several million colors.

Experts don’t have a method that can reliably test for tetrachromacy, which makes determining how common it is very difficult. That might seem strange because, if you search the internet for how to tell if you have tetrachromacy, you’ll find yourself awash in sites offering a quick, easy test. But there’s no way to test for tetrachromacy online, so none of those tests are legitimate.

How does tetrachromacy work?

People with tetrachromacy have an extra cone that helps them process and distinguish more colors. Most people have these three types of cones:

• Red (L). Red has a long wavelength, so these are called L cones.
• Green (M). This is in the middle of the visible spectrum, with a medium wavelength. That’s why they’re known as M cones.
• Blue (S). Blue has a shorter wavelength, so these are called S cones.

In people with tetrachromacy, the fourth type of cone is usually most sensitive somewhere in the realm of orange. That fourth cone type happens because of a genetic mutation (change).

So, why does a fourth cone make color vision so much more sensitive?

The fourth type of cone photoreceptor collects color information that’s similar — but not the same — as information from the other cones. Your brain processes the different color information and uses it to boost your color sensitivity. That’s why people with tetrachromacy can see hundreds of times more colors.

Why do people develop the fourth cone?

The gene responsible for the L cone is on the X chromosome. If you’re assigned male at birth (AMAB), you only have one X chromosome, so a mutation there will change all your L cones, causing some form of color blindness.

But people AFAB have two copies of the X chromosome. So, if you’re AFAB with a mutated copy of the gene, that means you can have both normal and mutated L cones. That happens in about 12% of people AFAB. Not all those people will have true tetrachromacy though., That’s because there are two things that must also happen:

• The fourth cone has to have a different frequency sensitivity. If it isn’t different, your brain doesn’t get enough information from the extra cone type to boost color sensitivity.
• You need four color channels to process all the color information. Human brains usually only have three color channels. If you have a fourth cone type but only three color channels, you can’t process and benefit from that extra color information.

People with four types of cones and three color channels can still have a “weak” form of tetrachromacy. Having that means they usually do better than average on color vision tests. But more research is necessary to confirm if weak/strong levels of tetrachromacy truly exist and how they work.

How do legitimate tetrachromacy tests work?

A key tool that researchers use to test for tetrachromacy is DNA testing. Researchers know which genes control how cones in your eyes work. That also means they know where to look for mutations and a few specific mutations that are the most likely cause.

But DNA testing alone isn’t enough to confirm if you have tetrachromacy. It also takes highly specialized, expensive hardware to do it. Testing also needs to happen in environments where lighting won’t throw off the results. This usually happens at research centers and hospitals that are part of or partnered with universities.

Can I take an online test?

There are no legitimate online tests for tetrachromacy, and it’s impossible to test for it using most computers and technology. Simply put, most devices can’t physically show colors in a way that only people with tetrachromacy could see.

Screens in virtually all consumer-level devices that can access the Internet, including desktop and laptop PCs, tablets and smartphones, all involve displays that have only three color channels: Red, green and blue (just like the cones in most peoples’ retinas). Those channels are most common because they’re what most peoples’ eyes can work best with. But because modern displays can’t show a fourth color channel, they’re no good for testing if you have tetrachromacy.

And color sensitivity tests online are unreliable at best. That’s because it takes extremely precise calibration of the monitor/display you’re using for those tests to be accurate. And even the color of the room you’re in can throw that off.

What do people with tetrachromacy see?

People with weak tetrachromacy have better-than-average color vision. But people with true (strong) tetrachromacy have extraordinary color sensitivity. At minimum, they see hundreds of times more colors than the average person.

To put this into context, think about people who have dichromacy. Even with only two types of cones, they can still see about 10,000 colors. Trichromats, which is what most people are, can see between 1 million and 10 million colors. That’s between 100 and 1,000 more colors than dichromats.

It’s also important to keep in mind that the way you see colors is subjective. That means you see colors in a way that’s very individual and specific to you. Research confirms that’s the case even for people without color vision differences or conditions. And that’s one reason people may not always agree things are the same color (either in person or in the occasional viral internet or social media post making the rounds).

A note from Cleveland Clinic

How do you know if you have tetrachromacy? Unfortunately, there’s no easy answer to that question. Online tests can’t answer this question for you, no matter how much they promise they can. Only people assigned female at birth can have tetrachromacy to begin with. And true tetrachromacy is so rare, there are only a few confirmed cases.

If you think you have tetrachromacy, the only way to be sure is to undergo specialized testing with scientific researchers. And if you find out you do have strong tetrachromacy, you may want to stop and take in your surroundings. You can take in every color, shade and hue in a way that most people can never experience or understand.