So Kingpin was black in the movie? Given Kingpin's origin and background, it really doesn't matter what color he is. He grew up a poor boy in the Bronx, he's just as likely to be white as he is black.
The reason most Marvel Comics characters are white is because they were created in the 1960's by white guys in a very segregated society. Either that or they were retconned 40's characters that were all apple pie red-blooded blond haired blue eyed white guys. The insurgance of black characters happened in the 70's because of the Blaxploitation craze. As a result, characters like Luke Cage, Falcon, Living Lightening, Black Goliath etc. were mostly black characters written by inept white guys trying to make a quick buck. The first respectable black character (IMO) was Black Panther, introduced by Jack Kirby in the 60's. They waited 10 years before giving him his own title, which was largly campy (although it can be argued most comics were in those days), but wasn't as Blaxploitive. Most black characters didn't hit any sort of respectable stride until the 80's and 90's.
Does it matter if Kingpin is black? No it doesn't since New York is such a messed up melting pot of ethnicities, it would be just as likely for him to be a poor white boy, or a poor african american boy.