Any special reasons?
Probably because, at least when I bought mine (late 2006), you had to get the more expensive MB to get it in black and most people buying MacBooks just got the base model (like how the 13" MBP base is most likely a much bigger seller than the upgraded version). Not only that, with the model I have at least, if you outfitted a white MacBook to have the exact same specs as the black one, the white one was slightly cheaper. You were basically paying extra just for the color.
I remember this as well. Pretty sure it was around $100 more just for the black color when having the exact same specs on the black vs. white. Crazy!