Kittens' eyes change color permanently by three months of age. The eye color of most newborn kittens is a shade of blue. Once permanent, colors range from brown to green.
Kittens' eye colors fluctuate between three to eight weeks of age. Colors range from amber to orange during this stage. When colors continue to fluctuate well past three months of age, the young cat may be experiencing health problems. Colors that indicate illness can include dark yellow, red-orange and dark brown. An eye color that's a shade of blue may be a sign of blindness or an eye injury in cats. Some cat conditions that list eye color change as a symptom include feline leukemia, uveitis and other infections. Some of these ailments are fatal. A veterinarian should be consulted when an adult cat's eye color changes rapidly.
When a cat has a different eye color in each eye, the result is known as complete heterochromia. The condition typically manifests as a blue eye with a brown, green or yellow eye. Any type of cat can develop complete heterochromia, but it most commonly occurs in cats with white fur. Until their eyes change permanently, kittens with heterochromia feature a different shade of blue in each eye.