Here's some essential radio history to put my query into context.
When NBC (National Broadcasting Company) came into being in 1926, it had a defacto monopoly in the realm of network radio until CBS and Mutual came along.
Due to NBC's power (a consortium formed by RCA, GE and Westinghouse), it had a powerhouse lineup of affiliates across the country and more programming than could fit on just one network. Thus, it divided itself into the NBC Red and NBC Blue network. The names had nothing to do with politics but were the colors of the thumbtacks used on the national map to denote the location of each affiliate.
Typically the big budget entertainment programs aired on NBC Red with the news, commentaries and dance band programs on NBC Blue (one of which was Walter Winchell, who morphed from a dance band announcer to a commentator).
The duopoly with NBC Red and Blue remained until 1943 when NBC spun off Blue, which eventually became ABC.
