Well, it would be consistent to use 'Black' for black Americans, and 'black' for black people in general, and likewise 'White' for white Americans, and 'white' for white people in general.

But then articles should use, based on context, both 'Black' and 'White', or both 'black' and 'white', while rarely it makes sense to use 'Black' and 'white' in one article, but that is the pattern used by newspapers.