Something interesting that I read a while back-
Blue eyes are recessive, genetically, to brown eyes, which means that if a brown-eyed person and a blue-eyed person have a child, that child's eyes will be brown, whereas if two blue-eyed people have a child, that child's eyes will be blue.
According to the article I read, blue-eyed males have a strong preference for blue-eyed women, because it serves as a visual test (upon having a child) as to whether she has been faithful (because if she got pregnant by a brown-eyed man, it'll be obvious). Brown-eyed men, on the other hand, since their eye color is dominant and will override anything else, have no such preference.
In practice, it might not always go that way, but since I saw something of a shift towards blue eyes in male responses (and towards brown eyes in female responses), I thought I'd share some background information. Either way, it's neat to think about how genetics influence behavior.