I'm sure there are probably blonde guys that are interested in dating black girls. I think it is more about individual preference.
There's also that thing that a lot of guys have about blondes - like they automatically think blonde girls are more attractive. That's probably due to how society has generally portrayed blonde girls...a blonde hair, blue eyed girl is supposed to be the perfect American girl.
My question for you is...do you really care? The fact that you are open to dating black and white guys tells me you are an open person that can see beyond color, whether race or hair color. So please don't get stuck on what may be lack of openness in others.
Besides, if you ask me (and a lot of other females as well), tall, dark and handsome is the way to go. :-)