Why do you think when a white woman dates a blk guy he is usually dark not lighter?

In all of my life from what I have seen from the people I know of to perfect strangers most black men with white women are medium dark to quite dark brown. If you look back and look around you may rarely see light brown or even lighter complected black men with whites. I can count on one hand the times I have seen a "red bone" black man with a white woman. I also noticed that when white men date black women, while the girl is not very dark she is a medium (regular) brown and not a "red" or "yellow" black chick. Those black chicks tend to gravitate to black men darker than them...interesting! One of my closest friends is Caucasian and she and her very dark complected black boyfriend have a newborn daughter. IR reproduction is so damn common in these parts. Haha.