Sometime you might see a cat with one blue eye and the other orange, copper, green or yellow. There is nothing wrong with the cute little critter; the two different colored eyes are a genetic tweak. Cats with eyes of two colors can see just as well as "regular" cats.
The scientific name for odd eyes is heterochromia iridis and can occur in other species including dogs and humans. Eye color is determined by the amount of melanin pigment in the eye. In cats with the white or white-spotted gene, the melanin is often prevented from reaching one eye, so that one will remain blue, while the other eye receives melanin and changes to green, yellow, amber or another color. The phenomenon is seen most frequently in white cats.
Kittens are always born with their eyes closed; when they open after a week or so, they are always blue. As the kitten develops, granules of melanin move into the iris and the color changes. If a kitten is going to be odd-eyed as an adult if you look closely you will see that the shades of blue in each eye are different from each other. One eye will remain the same and the other will gradually change to its adult color.
White cats are more prone to different-colored eyes than cats of other colors, and several breeds are prone to have odd eyes. These include the Turkish Van, Turkish Angora, Oriental shorthair, Japanese bobtail, Sphynx, Persian and Khao Manee. Turkey has had a program for many decades to preserve and protect Turkish Angora cats that are pure white and have one blue eye and one amber eye. These are highly prized and regarded as a national treasure.
There is a common misconception that cats with different colored eyes are deaf. This is not accurate. Around 30 percent of odd-eyed cats have hearing problems -- and the deafness occurs in the ear above the blue eye. In cats with normal eyes, the rate of hearing problems is about 10 percent to 20 percent. An interesting side-effect of odd eyes is that in flash photographs the blue eye will give a red-eye effect where the other is more likely to show with a greenish tinge.