That is a tough situation when it comes to racial identity. I think that if you expose them to both cultures enough and let them be around a lot of people--not just black or white, then the kids won't be confused with what race they should identify with more. They would feel like a person rather than a race.
Sometimes they may act according to how they look and are treated. If they look more white, people tend treat them like they are and the kid might be more comfortable in that world, and vice versa if they look more black. And then sometimes it doesn't matter at all. He/she will be whoever they want to be.
I guess the best thing to do is just emphasize personality and individuality rather than letting race define them as a person. And remember, as long as they have loving parents, it shouldn't be a bother them too much