Eye color, or iris pigmentation, is classified as being one of six colors: amber, blue, brown, gray, green, hazel, or red. Eye color is determined by genetics, which controls the amount of melanin (pigment) in the iris (the colored part of the eye). There are up to 16 different genes that play a role in determining eye color, though there are two main genes that most significantly influence eye color.
The amount of melanin in the iris, the colored part of the eye, determines what color a person's eyes will be. Genetics control how much melanin a person has in their body. When babies are born, and especially when fair skinned, the eyes are light colored because they have very little melanin in their eyes. That's because while in the womb the eyes don't produce much, if any, melanin. However, after birth, light stimulates the production of melanin; which is why the eye color may darken or change over time. Typically, the most significant change in eye color will take place in the first 6 to 9 months of life. By 12 months of age, most babies have their permanent eye color. Although some children's eye color may change up to 6 years of age, though this is rare.
It is interesting to note that the only pigment we have in the eye is brown. It is the amount of that pigment that determines if a person's eyes will be light or dark. There is no gray, green, blue or hazel pigment present in the eye. Technically speaking, everyone with the exception of those with albinism have the same eye color. The differences in eye color result from the amount and type of melanin in the front layer of the iris and how light interacts with it. Pheomelanin appears more red and yellow. Enumelanin appears more brown or black. For example, brown eyes have a heavy melanin presence on the front layer of the iris while blue eyes have a light melanin presence on the front layer of the iris; and both brown and blue eyes have the dominant pigment type of eumelanin.
What is the rarest human eye color?
This opinion can vary in different geographical areas. Though world-wide green-eyed and amber-eyed people are both extremely rare, with approximately 2% of the world's population having green eyes. However, if you look at the eye as a whole (not just the color given off by the iris), then violet eye color would be considered even more rare than green or amber eyes. Contrary to popular belief, true black eyes do not exist. Some individuals with a lot of melanin in their eyes may appear to have black eyes depending on light conditions. However, this is not truly black eyes but rather very dark brown eyes. Also, quite unusual, is the incidence of one eye being a completely different color than the other eye. This is called heterochromia and results from uneven melanin content between the two eyes.
The biology behind eye color:
Amber eye color is very rare world-wide, though most common in Asia and South American countries. Amber eye color ranges from golden yellow to a more copper tone.
Blue eyes are genetically recessive, and therefore much less common world-wide and are becoming rarer and rarer. It is estimated that approximately 8% of the world's population has blue eyes. Blue-eyed people have little to no melanin on the front layer of the eye.
Brown eyes are the most common eye color world-wide, with over 55% of the world's population having brown eyes. Brown eye color is also a dominant genetic trait.
Gray eyes are thought to have an even smaller amount of melanin than blue eyes. As a result, gray eyes are often classified as light blue eyes. Gray eye color appears to change color from gray to blue to green depending on clothing and light conditions.
Green eye color is the least common eye color, and is often confused with hazel eye color. It is estimated that only 2% of the world's population has green colored eyes.
Hazel eyes consist of shades of brown and green. Much like gray eyes, hazel eyes appear to change color from green to light brown to gold. It is estimated that 5-8% of the world's population has hazel colored eyes.
Red eyes do not appear naturally in humans, and are often referred to as pink eyes, and are present in individuals with albinism. This coloration exists because there is so little melanin in the eyes, there is nothing to conceal the blood vessels below.
Silver eye color is also quite rare, although silver eyes are considered to be a variation of blue eye color. Silver eye color is the result of a low amount of melanin (pigmentation) in the eye, which results in a gray-silver appearance.
Violet eyes appear violet when the red of the blood vessels at the back of the retina combines with the bluish color of the iris. People with albinism are often considered to have violet eyes. People with albinism lack pigment in their iris, so light can bounce off the back of the eye and then exit the eye.
Why does eye color appear to change?
Many people with blue, green or hazel eyes commonly notice that their eyes change color. This change in eye color depends on:
This is because blue and green eyes get their color from the quality and quantity of light, not from melanin (pigment).
Can eye color be changed naturally?
Other than a baby's eye color changing during the first year of life, eye color is permanent. Eye color remains the same and the only way to change appearance of eye color is through clothing, lighting, makeup or colored contact lenses.