Eye colors are determined by the amount and type of pigments in the iris, the colored part, of the eye. Eye colors are inherited traits that are influenced by more than one gene.
In humans, there are three genes than determine eye colors. These are called EYCL1, EYCL2, and EYCL3. They account for the three eye colors brown, green, and blue.
The perception of eye color depends on many different factors. The surrounding light and colors around the eyes can make the eyes appear to be different colors.
Because eye colors actually exist in many different varying colors, from the darkest shades of brown to the lightest shades of blue, a standard classification system was invented for research purposes based on the main iris color (brown, light brown, green, gray, and blue) as well as the amount of brown or yellow pigment that is present.
There main eye colors include brown, hazel, amber, green, gray, blue, and violet.
Brown Eye Color
Brown eyes contain large amounts of melanin, which absorbs light. Some dark brown irises with lots of melanin may appear black. Brown eye color is the most common eye color.
In many populations around the world, it is the only eye color that exists. Groups of people that are of non-European ancestry generally have darker eyes. This includes inhabitants of Africa, Asia, and the Americas. While brown eyes are also found in Europe and North America, they are not as predominant as in the non-European populations.
Hazel Eye Color
Hazel eye color has a moderate amount of melanin. Studies that have been conducted label hazel as the color between brown and blue. Often, the effects of hazel eyes produce an iris that is brown near the pupil and green near the outer edges.
It can be difficult defining the eye color hazel because is sometimes considered to be the same as brownish shades as well as green tones. Hazel eyes have also been described as light brown or even yellowish brown.
Amber Eye Color
Amber or yellow eyes appear to have a yellow/golden tint with a hint of copper. This most likely is due to the yellow pigment called lipochrome in the iris, which is also found in green and in violet eyes. Amber eyes are rare in humans though, but are common in animals, particularly cats.
Green Eye Color
Green eyes also have moderate amounts of melanin. Green eyes have been linked to brown hair color.
Green eye color is most often found in people of Celtic, Germanic, or Slavic descent, and even southern Europe descent, although it is much less common. Green eyes can also found among Caucasian populations in the Middle East and South Asia.
Gray Eye Color
Gray eyes are a variation of blue eyes. However, gray eyes may indicate the prescence of a uveitis, which is an inflammation in the middle layers of the eye.
Blue Eye Color
Blue eyes have low amounts of melanin. This eye color is pretty common in people of Europe and European descent, particularly northern European and eastern European descent. Blue eyes are slightly less common in people of southern Europe, the Middle East, and Central Asia.
The countries of Finland and Lithuania have the highest percentages of blue-eyed people, both with at least 80%. Ireland and Great Britain also have amounts of blue-eyed people, about 70% and 60% respectively.
Many babies have blue eyes that darken as they become older. This is because melanin production increases during the first few years of life. Eye color is usually stabilized by the aged of 6.
Violet Eye Color
Violet eyes are quite rare. Violet eyes are thought to occur due to the mixing of red and blue reflections. Few people have violet eyes. Some albinos have eyes that appear to be violet.