Truly awesome post at Fast Co Design where they have mapped racial diversity in several cities. A sample (there isn't one for Dallas unfortunately -- that I have found):
Bay Area. Quite a bit more diverse.
New York. In the source post, the author astutely points out that while NYC is mostly pockets of single race neighborhoods, the density and the measurable "borders" create areas of very potent cross-cultural pollenization.
San Antonio. The closest thing we get to Dallas.