There’s a wikipedia article titled “red states and blue states” that does a fair job of explaining it.
NBC covered election night in 1976 with a board that lit wins fir Carter (D) in red and wins for Ford (R) in blue. In 1980. The other networks use light-up boards and graphics and most followed the D=red and R=blue scheme. This went on until roughly 1996. There were some color change-ups and some networks did have R=red and D=blue graphics.
In 2000, the networks agreed (and all media have followec since) to a consistent red for Republicans and blue for Democrats scheme. The “switch” so many have noticed.
The ho-hum rationale they share is that “since Republican and ‘red’ both begin with an ‘R’, it’s just easy to remember that.” I think the media wants to use the current color scheme to depict Republucans as angry, violent, “rebels” (like the Confederacy and their battle flag) while themselves and Democrats as long-suffering but indefatigable Union-loving “yankees.”
More universally, socialist and left-leaning parties have traditionally favored red as the color to represent their movements. Conservatives and more right-leaning parties have traditionally favored blue. I think that was the unstated rationale in 1976. But, dur to the obvious bad associations with the color red, the media has flipped the colors to make the right look bad.
Nevertheless, the Right has largely decided it’s better to embrace the change than argue about it.
Well, I see in the time I wrote my screed, the qustion was sufficiently and effectively answered!
I Drive a Red Dodge Challenger if that means anything.
I had “TRUMP 45” Vanity Plates on it when I lived in CA.
https://www.youtube.com/watch?v=BqpJvey-7-s