Join me for a short adventure into feline biology as we discover what determines the color of the eyes. Let’s assume that a kitten was born in our family today, and her name is Layla. The area of Layla’s eyes that contains color is called the iris. This part has two layers of cells called melanocytes, which produce a type of pigment called melanin.
Since these cells that produce melanin are not active in young kittens yet, we don’t see distinct colors. This is why Layla is born with the same color in her eyes as all the other newborn kittens in the world: blue. Indeed, all kittens have blue eyes. Why blue, you ask? Simply because that is the default color that we see when there is no pigment present.
When can you see a kitten’s eye color?
As Layla grows, those cells that we mentioned earlier will start to produce pigment. Not much at first, but melanin production will ramp up quickly after a few weeks.
The color that we see when looking at an iris is determined by the amount of pigment that reflects sunlight. If sufficient pigment is produced, the default blue that Layla had as a kitten will slowly be replaced by a different color as the matured iris starts to emerge.
So how long does this process take? You should be able to notice the first changes about four to six weeks after birth. The entire transformation is usually completed by the fifth month after birth.
Adult cat eye color
The type and amount of pigment are what determine the final color of the iris. There are darker and lighter colors, which correlate with the amount of pigment. For instance, when your cat has green eyes, that means there is not much pigment available in the iris. Blue is another relatively light color that we see when there is little melanin present.
Eye pigmentation is heavily influenced by genetics. So, if mom and dad had the right genes, there’s a decent chance any offspring will possess that color too. Note that this is never guaranteed.
In fact, some cats are born with such genetics that they can’t produce any pigment at all. In these cases, the eyes retain the same deep blue color throughout a kitten’s transition into adulthood.
Why do some cats have different colors in their left and right eye?
Not all cats have the same color in both eyes. This is what scientist refer to as heterochromia, a term which describes oddly colored irises. The phenomenon is most often observed in white and tuxedo cats. While this condition is usually a result of genetics, it may also result from damage to the melanin-producing cells during development.
Cats may also be dichromatic, which is another scientific term that’s used to describe eyes that contain two distinct colors instead of a single one (source). Some people find this look very aesthetically pleasing.