That's not true.

"Republicans have cut deals with opposing black Democratic state legislators to create majority-black districts. By packing black Democratic voters into a single district, they can essentially ensure the election of a black Congressman or re-election of a black state legislator due to the packed concentration of Democratic voters. However, the surrounding districts are more safely Republican in areas like the South, where white conservatives have increasingly shifted from the Democratic to the Republican Party in national elections in the last four decades."

"Bipartisan gerrymandering refers to redistricting that favors the incumbents in both the Democratic and Republican Parties. Bipartisan gerrymandering became a salient practice in the 2000 redistricting process, which created some of the most non-competitive redistricting plans in American history."
https://en.wikipedia.org/wiki/Gerrymandering_in_the_United_States