Eye colour.

[Fang]

I'm no optometrist but almost all of these examples display central partial heterochromia iridis. Apparently about .6% of the population have it (myself included), though that may be stats for complete heterochromia iridis, where each eye is a different colour.
It's nothing to celebrate (it won't give you superpowers or mean you're of fantastic cosmic heritage) but it is neat lol