Researchers found people who had vitiligo were less likely to have blue or grey eyes compared with people who did not. A 2012 review of research on vitiligo published in Nature found the autoimmune disorder, which causes a loss of skin color to mottled patches, was less prevalent in blue-eyed people. You are also a little more likely to have vitiligo, the pigmentation condition, in your skin compared with people who have lighter eyes. More importantly, those with lighter eyes are generally lighter-skinned as well, and therefore are generally at higher risk for skin cancer.

Also, while not directly related to eyesight, people who have grey, green, or blue eyes are generally light-skinned, and are generally at higher risk of skin cancers. Researchers have found that people with lighter-colored eyes (blue and green) tend to be less agreeable and more competitive than their brown-eyed peers. Even color combinations that are considered to be more uncommon, such as amber and gray, are more technically common than green eyes. The most common color for eyes is brown, the second-most common is blue or grey, and the least common, or rarest, is green.

Granted, brown is the worlds most common eye color, but a few shades that we commonly consider when talking about our own eyes are blue, hazel, and green. Blue eyes contain less melanin than brown, but both colors are relatively common around the world. More melanin in your iris means a brown eye, whereas less can mean a blue, hazel, green, or grey eye.

People with darker brown eyes have more melanin on the posterior layers of the iris, and eyes with very little melanin (or none) on the anterior layers of the iris look more blue, green, or even hazel. People with brown eyes have more melanin in their iris, which insulates connections between brain cells and may make them fire faster than their lighter-eyed counterparts. Your lighter eyes also offer less UV protection than your brown eyes, meaning that you are at higher risk for ocular melanoma.

People who have green eyes, and others that are lighter in color, generally have higher eye cancer risks, especially for intraocular melanoma. Lighter eye colors are also associated with a higher risk for macular degeneration, which causes the central field of vision to become lost, and for ocular melanoma (cancers that occur in or around your eyes). Because lighter eyes have less pigmentation that can protect them against harmful UV light, it is true that lighter-eyed people have an increased risk of lifetime uveal melanoma, the middle layer of your eyes, than their darker-eyed peers.

For instance, brown-eyed individuals are said to be at lower risk of developing eye cancer, diabetic retinopathy, and macular degeneration, but at higher risk for cataracts, as opposed to those who are lighter-eyed. For instance, if one parent has brown eyes while another has blue eyes, the chances are higher that the children of the parents will have brown eyes. For example, if one eye is green while another is brown, blue, or some other color, then you have total heterochromia.

People with this condition can have a variety of colors inside one eye (for example, an iris can have half of one color and half of another). If you have had an injury to your eye, the damage to your iris may have caused a loss of tissue, making your eye look like a different color. Usually occurring only in one eye, this condition causes iris color change, with only one eye losing pigment.

There are times that an eye can look a different color, but there are explanations outside of emotion. Depending on factors such as lighting and attire, grey eyes can look differently. Some eyes may even have spots or patches mixed with darker or lighter colors.

One study found that those who had lighter colored eyes were smarter, and they generally did better academically, compared with those who had darker eyes. A 2014 study concluded that women with light-colored eyes are better at withstanding pain in pregnancy compared with darker-eyed women. Women with lighter-colored eyes can have higher pain tolerance, according to a study by APS, and lower risks of anxiety and depression, especially during labor and postpartum.

Your hazel eyes could mean that you are more prone to pain and anxiety than women with lighter-colored eyes, according to the APS study, which lumped women with hazel eyes and those with brown eyes together in one category, darker-eyed. Darker-colored eyes may mean that you are at lower risk for skin cancer. If you have grey or green eyes, or you have heterochromia, anisocoria, or albinism, you could say with confidence that your eyes are uncommon.

Other studies have found people with blue or green eyes are at higher risk for melanomas in their eyes, probably because they have fewer light-absorbing pigments that protect eyes from sun damage. It is also possible for genes to make children have two different eye colors, like blue on the left and brown on the right. One symptom is an irregular pupil size, which may make you appear to have two different-colored eyes, explains Grover.

This is in contrast with the typical distribution of eye colors seen among non-Hispanic European-Americans without vitiligo, where 52% generally have blue or gray eyes, while just 27% have brown or pale brown eyes. Of the almost 3,000 vitiligo patients enrolled in the study — who were all Caucasians — 27 percent had blue eyes, 30 percent had green or hazel eyes, and 43 percent had brown eyes, while the typical eye color breakdown for Caucasians is 52 percent blue, 22 percent green or hazel, and 27 percent brown.