Democrats are strong in minority districts, but minorities do better in white districts running as Republicans. From Josh Kraushaar, writing in the National Journal:
It’s clear Democrats are a much more inclusive party—just look at the fact that nearly one-third of House Democrats are non-white. [But o]f the 75 black, Hispanic, and Asian-American Democrats in Congress and governorships, only nine represent majority-white constituencies—and that declines to six in 2011. . . And when you only look at members of Congress or governors elected by majority-white constituencies (in other words, most of the governorships [picture: Nikki Haley of South Carolina] and Senate seats, and 337 out of 435 House seats), Democrats trail Republicans in minority representation.