Ever notice some cats have two different colored eyes? I've been noticing this "problem" a lot with the cats my parents own. I like it though, it looks awesome and it makes the cat look unique. Seriously look at it. So adorable!
In order to understand why some cats have different color eyes, we must first understand what melanin is. Melanin is a pigment, that comes in two different forms: eumelanin and pheomelanin. Eumelanin is black or brown, pheomelanin is yellow or red. Melanin is responsible for our skin color, hair color, our eye color, even the color of feathers and scales. Darker colors have more melanin than lighter colors do.
Most kittens are born with blue eyes, because they aren't born with the color pigmentation they need for their true eye color. By the time most kittens reach around the age of 3 months most kittens have their true eye color. Melanin moves into the iris of the eye, and changes the color to whatever is its true eye color, but sometimes melanin only reaches one of the eyes, which means the eye without the melanin pigment will remain blue. This is technically called heterochromia.
Heterochromia occurs most commonly in cats with the "white gene". Basically the white gene makes it hard for the melanin pigment to move into the cats eye. Although, heterochromia can occur with any color cat.
