One of the cleverest things the progressive media has done is to take the color blue as their own. It was always communists who were identified with red: Red China, better dead than red, Red Square. They stole blue and assigned red to conservatives and conservatives didn’t fight back so now we are red.
They weren’t set prior to the 2000 election but after it was red for the pubs and blue for the dims. It wasn’t a hard and fast rule but IIRC some of the networks used blue for the incumbent party and red for the challenging party on electoral maps. That was how it was for 2000 but for some reason maybe because that election was so contentious the colours became permanent.