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Kittens start developing their eye color around 6-7 weeks old as melanin, the pigment responsible for eye color, kicks in.
The lack of significant melanin production in the eyes gives colorpoint cats like Siamese, Himalayan, and Ragdoll cats their characteristic blue hue.
The KIT gene can lead to blue eyes, cats with mismatched eye colors (known as odd-eyed), and a higher rate of hearing impairment in white cats.