Iris

Our kids have blue eyes (and yes, they are blond), my eyes are blue-ish blended with other colours. But:
D's eyes though are brown!
This is weird, because AFAIK brown is dominant, blue is recessive. 79% of people have brown(-ish) eyes.
So what would be the expected colour of a mix of brown and blue? Right: brown! But not in our kids. According to Charles Davenport (eugenicist) this would have been impossible. But luckily the experts discovered he was not completely right, it is not just one gene that determines the eye colour. Even if both parents have brown eyes, their kids can have blue eyes. Nature is not binary.
Thanks to dbifulco for hosting the Tiny Tuesday challenge in August.