The colors change from time to time. '68 was the first election I watched, and from then until '80, Republican was Blue, and Democrat was Red.
Then all three networks changed in '84. I don't recall ever hearing why, but it was my guess that since Reagan was such an anti-communist, the nets wanted to avoid associating the color Red with the Democrats' anti-anti-communism.
Been Red Reps and Blue Dems ever since.