There are many ways to feel special. Maybe you’re a stellar athlete. Maybe you excel at your job. Or maybe you have a unique physical trait like a rare eye color.

There are four main eye colors in the human population. These are brown, blue, hazel and green. We talked with an ophthalmologist at ORA Vision in Atlanta, to find out how common each eye color is – and which one is the rarest of them all.

The rarest eye color is green, according to the American Academy of Ophthalmology. Only two percent of the global population has green eyes.

Green is also the rarest eye color in America. A 2014 survey by the Academy found that 45 percent of Americans had brown eyes, 27 percent had blue eyes, 18 percent had hazel eyes and nine percent had green eyes. The survey also found that 1 percent had eyes that were a color not listed.

Every iris contains a pigment called melanin, but the amount of melanin varies from person to person. No person has the exact same amount of melanin in their irises.

The amount of melanin in your iris determines your eye color. “It’s all about the internal reflection of light proportional to the amount of melanin. It’s not really that the iris is … green, its actually that the amount of melanin that that iris has is reflecting a color and it happens to be green in color.”

Brown eyes have the most melanin, and blue eyes have the least amount of melanin. The amount of melanin in green irises is somewhere between blue eyes and brown eyes. This amount is the least common you can have. Experts don’t have a reason for why exactly that’s the case.