Grey eyes make up about 3 percent of the world's population—the second rarest eye color. There are also rare cases of violet and red-colored eyes.

Did you know some people have red eyes? How about violet? We spoke to an optometrist to learn how rare some eye colors are ...

Red is the rarest hair color, but to understand why that’s the case, you need a basic grasp of the science. There’s a lot more to it than the simple traits we learned about in high school biology.