The Washington Post has a pair of fascinating articles on shifting residential demographics in the DC area. The first documents the decline of White enclaves in the region. The second looks at the rise of the overwhelmingly Black and very wealthy Prince George's County.
How does this work? Well, it seems that (at least in the DC area), barriers to minority groups moving to White neighborhoods are finally starting to crumble, and when members of other racial groups move in, Whites aren't moving out. That being said, Whites still aren't willing to affirmatively move into neighborhoods that are predominantly non-White, which allows spaces like PG County to continue serving as Black enclaves.
Anyway, they're both good reads. Highly recommended.
UPDATE: Ta-Nehisi Coates has characteristically great thoughts.