Brown, blue and green eyes are the "standard" eye colors, but we've all seen people with even different eye colors. There's also gray, "hazel", a mixed brown/green/blue, golden brown or amber, even violet. Many children are born with non-descript gray eyes and some become blue, some brown. How much do we really know about eye color?

Eye color is determined primarily by the concentration and distribution of melanin pigment on the iris fibers. The iris is located inside the eye, between the cornea and the internal crystalline lens. The hole in the middle is called the pupil and it changes size to regulate the amount of light entering the eye. If the iris contains pigment on both the front and back surface, the incident light that reflects off the iris is brown. Sometimes there is little or no pigment on the front surface.

The light interacts with the gray iris fibers and the iris stromal cells and reflects as blue. The size and spacing of the fibers and stromal cells determines the "blueness" or "greenness" of the reflected light.

People from different countries have different eye color, according to their origin:

Brown - Inhabitants indigenous to Africa, Asia and the Americas generally have brown eyes. Brown eyes are equally found in Europe and Oceania, though within some European populations they are not predominant to the same extent.

Hazel - Hazel is mostly found in some regions of the Americas and Europe. Very rarely, hazel eyes can be found in populations of The Middle East, and of people with African or Asian descent. In North America, "hazel" is often used to describe eyes that appear to change color, ranging from light brown to green and even gray, depending on current lighting in the environment.

Green - Green eyes are the product of moderate amounts of melanin. They are most often found among people of North and Eastern European descent, and to a slightly lesser extent, in Southern Europe, and parts of Central and South Asia.

Blue - Blue eyes are relatively common throughout Europe and other areas with populations of European descent, such as the Americas and Oceania. While they are most common among people of Finno-Ugric descent, there are also rare populations in Central and South Asia that have fairly uncommon natural occurrences of blue eyes. Ireland is the country with the highest proportion of blue-eyed people. Finland, Lithuania, Latvia and Estonia also have high proportions of blue-eyed people; it is also very common in other countries in Northwestern Europe, including the Netherlands, Germany and Britain.

There's a rare genetic condition called albinism in which those individuals do not have pigment on the back of the iris and their iris color appears pink. Sometimes, the pigment from the back surface “rolls” up onto the front surface right at the pupil border. This results in a brown ring around the pupil, which can look quite unusual in an otherwise “blue” eye. Although the majority of irises have similar pigment density on the back surface, some people have less and that allows for some reflection from the retina in the back of the eye. The retina reflects red from the network of blood vessels contained within its structure. This is also what causes the red reflex in the iris pupil seen in photographs taken with a flash. The red color interacts with the blues and browns to create aqua and violet iris colors.

However people often use contact-lenses to change their usual eye color. Many people refer to cosmetic contact lenses as theatrical lenses, because they are often used to add to special effects and are used only a short time by the wearer for a theater or movie production. Cosmetic contact lenses can also be worn to give a Halloween costume an extra spooky effect, and to make it stand out from the crowd. Another word for these types of lenses is non-corrective lenses. They can look like cat's eyes, aliens, animal print, solid colors, all white, all black, or even camouflage. No matter what, cosmetic contact lenses can really make a huge impact on one's appearance.

Some famous examples of people wearing cosmetic contact lenses are singer Marilyn Manson and several instances in Star Wars Episode I when Darth Maul would turn evil. These types of lenses can make anyone look scarier or more evil. There are even cosmetic contact lenses out now that can resemble exact replicas of certain anime character's eyes. They are all the rage in Japan and are becoming more and more popular in the United States as well.

Most people wear contact lenses to help them see more clearly and avoid having to wear eye glasses. Some people buy cosmetic contact lenses. These specially made lenses can come in a huge assortment of colors, patterns, and designs. They are specifically made for looks only, which is why they have earned the title of cosmetic contact lenses.

An interesting question about changes in adult eye color is often asked. As we have discussed previously, eye color is about reflection of ambient light from the structure of the iris. People with lightly colored irises note that their eye color changes according to the colors they wear. No mystery there, but the resultant apparent color of the eye is a combination of the color reflected from one's clothing (or even eye make up) and is not always what you might expect!

Some people have noted that when they are ill or under stress that their eye color becomes darker or lighter. Clearly there has been a change in the distribution and/or density of melanin or lipofuscin on the iris. How this actually occurs is not fully understood, but we are beginning to have some clues as to the processes. A recent medication used to treat glaucoma, latanoprost, causes such a color change. We understand, at least partially, the mechanism of action of the drug, a prostaglandin analog, which means it mimics this hormone, which is normally present in the body. It would appear, then that hormones may have effect iris pigmentation and this might explain the change in eye color sometimes seen in adults. It should be mentioned that there are certain specific systemic and eye diseases that can cause a change in iris color and any marked change of short period of time requires prompt medical attention.

People even celebrate Different Colored Eyes Day on 12th of July: it has two reasons to celebrate. First of all, it celebrates diversity of eye color. Wouldn't the world be boring, if everyone had the same color of eyes?

Secondly, it recognizes an eye condition called Heterochromia. One eye may be brown, while the other is blue. Famous people who have Heterochromia include David Bowie, Jane Seymour, and Christopher Walken.

Your eyes are an important part of your appearance. They are also important in communications. When you look into your lover's eyes, you need to like what you see. Making "eye contact" just wouldn't be the same without different colored eye. Isn't it great that we have a variety of eye colors to set us apart from one another?