Danny Boy
Hunlock Creek PA
2014

our Dad's beloved cat Danny Boy RIP

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.

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.

https://www.catster.com/lifestyle/cat-facts-siamese-cats-genes-albino-why-is-the-sky-blue