Colour #4: Pink, Olo and 4D colors

The real world isn’t single wavelength

The sun, being a massive ball of plasma, among basically any other white light source, will be emitting photons across the entire visible spectrum — whatever reaches our eye at any given moment will rarely be a single wavelength of photons, meaning we really need to look at the combined effect of multiple wavelengths hitting our cones.

This will create situations in which cones are stimulated in ways that single wavelength light cannot, leading to us seeing non-spectral colors.

Is pink a real color?

Look at the intersection of the S and L cones above. You will see that there is no single wavelength of color that will stimulate the S and L cones without also stimulating the M cone, because of lots of overlap.

But we can easily make it happen by shooting two photons into your eye at the same time, one on the blue end of the spectrum and one on the red end.

Your brain will get the signal, and it is left with no choice: It can’t really render cyan, because the M cone is not stimulated. It must be a distinct color, and I guess that’ll be pink!

Is pink a real color? Well. I guess I see pink flowers and pink sunsets and pink flamingos and pink cotton candy, so it must be, right? Even though it’s a concept that’s made up by our brains, it is a real color in the sense that it is a distinct perceptual experience that we can have.

Is olo a real color?

Stimulating just the S cone is easy, right? Just pick a wavelength in the short end of the spectrum — you will see a deep purple. Similarly, stimulating just the L cone can be achieved by picking a wavelength in long wavelength end of the spectrum, yielding a deep red.

But stimulating just the M cone is not possible without some heavy trickery, because it overlaps with the other cones everywhere.

Well, researchers at Berkeley have come up with trickery to do so in 2025: They mapped out people’s retinas to identify each S, M, and L cone inside, and then shot lasers at just the M cones. The new color was dubbed “olo”, which I hear comes from “010”.

Is it real? Well, it is a distinct perceptual experience that humans can have. The 5 people who have seen it have described it as a cyan that is more intense than any cyan they have ever seen before. There probably aren’t many olo-colored things in real life, but all I can say is that I’m jealous that I haven’t gotten to experience it yet!

Same colour, different light

There are infinitely different combinations of light that can produce the same color. Two sets of lights producing the same color are called metamers of each other.

The fact that we perceive light via three different detectors means that by just picking three wavelengths of light, preferably spaced out across the visible spectrum, we can mix any color that our eyes can see, even the non-spectral ones. This is what makes screens work!

Dichoptic Tetrachromacy

A particularly enterprising nerd called Ooquai has been building a pair of glasses with a filter on each eye. The left eye filters away all light > 610nm and the right eye filters away all light < 625nm, essentially giving him a fourth cone type that recognizes deep red light.

This gives him a fourth dimension of color vision, and many amazing opportunities to see more impossible colors like pink by stimulating each of the 4 cones in ways that are impossible with just 3. He calls this dichoptic tetrachromacy, and it is a fascinating way to explore the limits of human color perception.