My older brothers are both married to white women, and I'll also be married to one very soon. I don't know a whole lot a men my age who are mixed black and white... I know that it is becoming less and less taboo, but you still don't find many guys who are mixed black and white and are older than 20. With that being said, I don't know a single MB&W guy who is dating or has ever dated a woman who is darker than he is. Why is that the case? Perhaps I can suggest a few reasons.
1. Intimidation - Black women are different than white women... is that the understatement of the century? I don't want this to sound racist at all, but there's something much more scary about getting a black woman angry. When a white woman gets angry, it's funny... go give her a hug, and tell her that everything is going to be alright. Offer her some low-fat vanilla frozen yogurt, and pop in one of her "Friends" DVDs, preferably the episode where Rachel sees the prom video. Black women, however, are a much different story.
Go ahead, try to anger a black woman... I'll wait...
Are you still alive? An angry black woman will eat you alive and spit you out. If you hear a "mmm" you better brace yourself, if you hear a "no you didn't," run until you can't breathe anymore, and if she starts snapping her fingers and pulling her earrings off, say hi to God for me... because you're already dead. Black men know how to deal with this because they have mothers and sisters who are 100% black... which leads me to my second point.
2. Lack of experience with black women in the home. If you're a male, and you're mixed black and white, that means that your dad is black, and your mom is white. There's a few situations where it is the other way around, but I would say that 80-90% of MB&W guys have black dads. Because of that, they don't grow up in a home with black women, and they don't get the 18 years of experience needed to stand tall around a beautiful, strong, black woman. Black men, get a wealth of experience in this area, and the brunt of their experience comes from a common source... momma. If you're a black man, you already know what I'm talking about. If momma ain't happy, ain't nobody happy. You ain't happy, pops ain't happy, your siblings ain't happy, your dog ain't happy, your dead ancestors ain't happy. Along with that, if you're the reason why momma ain't happy, then you can only take comfort in the fact that she won't kill you. Everything else is fair game. While black children grow up, they're equipped with the necessary tools needed to make momma happy, and that's all that matters. Despite all of that, black men LOVE their mothers... it shouldn't be any other way. When black men are looking for a wife, they want a woman a lot like momma. In other words, they want a strong black woman... except for when the go for white women... which I won't complain about, because that's why I'm alive. MB&W men don't get the same exposure at an early age. It is like trying to learn Chinese at the age of 18 instead of from childhood.
Anyway, a MB&W man might not last very long in a relationship with a black woman. I don't know. I'm not acting like I know it all, but at least I have a little bit of insight from my experiences.