Everyone has different eye color, why is that?

Eye color is the color of the iris, the colored part around the pupil (the small black spot in the center of the eye). Fun fact: Everyone has a unique eye color, just like a fingerprint.

The most common eye color is brown, followed by blue, green, or hazel. The iris can also be a mixed color, such as brown with a golden hue, brown with a green hue, or brown with a blue hue.

The iris is located inside the eye, under a clear, colorless layer called the cornea that is less than half a millimeter thin. The iris is made up of many cells, specialized muscles, blood vessels, and nerves. Surrounding the iris is a slimy substance with millions of tiny fibers that crisscross each other.

The human body only produces brown iris pigment (melanin), not blue, green, or hazel iris pigment.

Iris pigment cells contain melanosomes. All iris colors have the same number of melanosomes, but the pigment granules inside the cells are different, for example brown irises have more pigment granules than blue irises.

Other cells of the iris make up the tiny fibers and mucus in the iris, which help protect the iris from damage. The pupil can contract or dilate thanks to special muscles of the iris with elastic fibers.

The back of the iris is a dark surface with cells filled with Posterior Surface Pigment that helps prevent light from scattering through the iris, which is good for vision.

White light contains a spectrum of rainbow colors from blue to red. When light passes through the iris, blue light scatters more than other colors and is reflected back. If there are fewer pigment particles, we will see that iris as blue.

Other colors of light, especially red, are scattered less and enter the iris between the fibers, mucus, and cells. Therefore, green, hazel, or brown eyes have more pigment granules that absorb this light.

Thus, it is the result of some colors scattering more or less light than others combined with the brown pigment particles absorbing more of some colors and the number of pigment particles that determines a person's eye color.

The color of the iris does not remain the same throughout life, but can change as darker pigments are produced in the iris cells after birth. For example, a baby with blue eyes can turn brown or hazel after just 1 day of age.

Certain diseases or injuries can also cause the color of the iris to change.

Some people are born with one brown eye and one blue eye, and this never changes throughout their lives. The cause of this is unknown.