I'm going to declare a black woman here and I'm happy for my hypothesis to be proved wrong, but be nice
I think your hypothesis is generally correct, chanie44 , but I can think of one notable film exception.
Ever seen Save the Last Dance with Julia Stiles, Sean Patrick Thomas and Kerry Washington? It was about an interracial teenage couple, white girl and black boy. They did a good amount of snogging, and it's strongly implied that they had intercourse.
One of the themes the film touched on, which I've seen raised elsewhere, is black women's anger when "the best" black men, i.e. the the hard workers, the professionals, the ones with integrity, the ones who are going somewhere in life, pair up with white women.
In addition, there's definitely a deep-seated aversion in the U.S. to black men being with white women. In the not-too-distant past, black men in the American South would get lynched for anything resembling sexual interest towards white women, whereas white slave-owners often slept with their black female slaves.
Here's an interesting article about which interracial couples spark the most outrage.
Save the Last Dance seems to be an exception among films, though, and it does seem that, in general, Hollywood blockbusters aren't keen to rock the boat too much, i.e. alienate large swathes of fans by putting interracial couples front and centre.