Move over, Isaac Newton. You might have invented the color wheel, but my Siamese cat is better equipped to explain why the sky is blue. And it’s not because he’s been hanging around physicists, either (which he does, by the way). It’s because of his eyes. Let me explain.

Newton can be blamed for something you probably heard in grade school, though: Roy G. Biv. And I’m not talking about some poor kid stuck with the worst name on the planet. I’m talking about the colors of the rainbow.

ROYGBIV = Red, Orange, Yellow, Green, Blue, Indigo, and Violet.

Newton identified five primary colors: red, yellow, blue, green, and violet. (This differs from modern color theory regarding pigment, which identifies red, yellow, and blue as primary.) He added orange and indigo to his color wheel so he’d have the same number of colors as there were musical notes in a scale (I swear it’s true — you can’t make this stuff up).

The colors are in that order based on their wavelength, red being longest at around 650 nanometers and blue/violet being the shortest, at around 400 nm.

Siamese genes

So what does that have to do with Siamese cats? You may have noticed that Siamese have blue eyes. That blue eye color is thanks to a special genetic allele they carry that causes a form of albinism. Wait — Siamese cats aren’t albinos.

Actually they are. Temperature-sensitive albinos.

This albinism is what causes breeds like Siamese, Burmese, Himalayans, and Tonkinese to have pointed coats — darker in the extremities and lighter in the torso. And this albinism extends to eye color, too.

Here’s how it works: There are two layers in the iris of the eye that determine what color your eyes are (this is true of humans as well as cats): the stroma and the epithelium.

In most cats, pigmented cells are scattered throughout both layers. But for cats with Siamese or Burmese alleles (gene pairs that cause temperature-sensitive albinism), there is no pigmentation — or color — in the stroma.

And whereas other cat breeds with blue eyes do have pigment in that lower epithelial layer, the blue of a Siamese is due to the absence of pigment in both layers.

Colors and wavelength

If there’s no color in a Siamese’s eyes, why do they appear blue? For the same reason the sky is blue.

It has to do with the fact that, of all the colors in the visible light spectrum, blue has the shortest wavelength, and colors with shorter wavelengths scatter more than colors with longer wavelengths — it’s called Rayleigh Scattering. Because blue light is the predominant light that is bouncing around in the stroma layer, that’s the color you see (as indicated by the cool red arrows bouncing around in the diagram above).

But wait. According to Isaac Newton — and the rainbow — the shortest wavelength is really the violet one. So why aren’t a cat’s eyes violet?

Again, for the same reason the sky doesn’t look violet to the naked eye. Human biology. Simply put, our eyes just don’t see that color very well. So blue wins.

Colors can change

Why does a Siamese’s blue eyes seems to change color? At the risk of being repetitive, look at the sky again. Have you ever heard someone comment about the sky being a “Colorado blue” on a particular day?

We’ve all experienced those crisp, clear days where the sky seems to be a richer, more stunning blue. Then there are days where the sky seems a bit more washed out.

“Colorado blue” refers to a day where there are fewer pollutants in the air. On days like that, there’s no smog or moisture in the air to absorb some of the light scattering, and so the blue comes through in a potent way.

The same holds true with the eyes of a Siamese.

In addition, because there’s no pigment in his eyes, surrounding color can reflect back into the eye, changing its color.

So there you have it: The Siamese cat is the walking, meowing mirror of why the sky on Earth is blue.

Read more cool cat science stuff by Lisa Richman:

About Lisa Richman: Writer, director, pilot, foodie, cat person. When she’s not on set, this director of film and video can usually be found taking photos of cats (and food) with her trusty Nikon, or cruising aloft at 3,000 feet. She’s cat mom to an opinionated Tonkinese, a hearing-impaired Siamese, and a feline fashionista. She’s also the owner of a recently launched food blog, and the Cat Writer’s 2014 Entertainment Blog, A Tonk’s Tail.