Seems they overlooked the fact that it was Republicans, especially conservatives such as Everett Dirksen (R-Ill.) who saved the Civil Rights act from being filibustered to death and that Barry Goldwater had pushed for the integration of the Phoenix airport in the 1950's.
Actually the permanent black switch was made in 1936.
They were 100% a majority GOP vote up to and including 1932, then they totally reversed that for the 1936 election and forward.
The change was instant, and total, and permanent.