The Red-Blue swap occurred during the 2000 election. Voter New Service did it so the MSM would be free of culpability. But VNS was a creation of the MSM. They all contributed to it and used its service.
Yeah the searing 2000 election made the colors permanent from that point on. Before that there wasn’t any consistency in colors. You could switch from one network to another and see opposite color schemes. That said I think one network said the idea pre 2000 was that one color represented the incumbant party and the other the challenging one. Again that would have flipped the colors over election cycles too.