You're right over the very short term, but when you bring up the child of a black man and white woman as a counter example, you clearly can't see the forest for the trees. You understand Mendelian genetics, but what you're missing is evolutionary pressure. The very fact that black man is having children with a white woman, and not with a black woman (who is likely single instead) means the evolutionary pressure is away from darker skin.
And about Europe, you totally mis-understood me. I didn't mean that Europe has become lighter skinned over the last two years or something, I meant the fact that "white people" come from Europe. White people evolved not because god created them or by random chance, but because 10,000 years ago it was all covered in ice so there wasn't much food around, men could only afford in Europe to have one wife. So their (Men's) preference for lighter skin lead to the evolution of white people in the first place.
Anyway I didn't mean to stir up a hornets nest, this is just something I've been thinking about and as a black person it bothers me... I guess it shouldn't since black white we're all people and if black people over generations become lighter so be it.
PS. If you want scientific sources there's plenty online:
http://www.sciencemag.org/cgi/content/summary/316/5823/364a