President Obama is putting aside politics-as-usual to honor a black Republican former senator today. Edward Brooke was the first popularly-elected black Senator (Reconstruction doesn't count) and the only black Senator since Reconstruction from a state other than Illinois (the others have been Carol Mosely-Braun, Barack Obama, and Roland Burris). He was elected as a black Republican in an overwhelmingly white and overwhelmingly Democratic state and was reelected to a second term, allowing him to serve in the Senate for over a decade. Today he's receiving the Congressional Gold Medal.
Redistricting in favor of majority-black districts has effectively created an environment that makes black senators much more rare than we would expect, since it tends to produce candidates who are focused on issues that energize black voters but who seem out of the mainstream enough to be much harder to win elections in statewide races. Democratic redistricting that relies on artificial lines to ensure majority black districts has ironically made it much more difficult for black politicians who are more electable statewide (and thus get into the Senate) from getting into the positions that very much help you to make such a statewide run. I've even seen conservative pundits (e.g. Abigail Thernstrom) claim that Republicans have gone along with this kind of gerrymandering because they knew it would ultimately favor their own party.
See Nate Silver's Why Are There No Black Senators? for a more substantial argument for the claim that gerrymandering of this sort is counterproductive to racial progress in the U.S. Senate. I think he's right.