They didn't adopt it, they were assigned it. For the Presidental elections, the television networks used the device of a map where each state's color signified who had "won" the electoral college votes for that state. Red, white and blue being the obvious colors, and the mnemonic "Red=Republican" set the choice.
Originally a big plexiglass stage set with colored light bulbs, but more recently video walls and computer graphics. I don't remember who (ABC/NBC/CBS) did it first, but the others copied it.
Mark Zenier snipped-for-privacy@eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)