Heterochromia is when a person has differently colored eyes or eyes that have more than one color. Most of the time, it doesn't cause any problems. It's often just a quirk caused by genes passed down from your parents or by something that happened when your eyes were forming.

What is the rarest eye color in the world?

The production of melanin in the iris is what influences eye color. More melanin produces a darker coloring, while less makes for lighter eyes. Green eyes are the rarest, but there exist anecdotal reports that gray eyes are even rarer. Eye color isn't just a superfluous part of your appearance.

How common is it to have two different colored eyes?

The instance of a person having two differently colored eyes is pretty uncommon, just 11 out of every 1,000 Americans. This uncanny trait is caused by several factors, and can actually develop over time.