For most of the past forty years, red represented Democrats and blue, Republicans. The reasons stem back to the soldiers of the north in our Civil War who were predominantly Republican and to the royal blue of Europe. The color red was associated with passion and socialism, characteristics more common to the Left. In the U.S., blue denoted those who put reason before empathy, an attribute more generally assigned to cold, blue-blooded Republicans, allegedly of the country club set.
While its ubiquity is relatively recent, the use of colors to depict states during Presidential elections dates back to the universal adoption of color televisions, around the mid 1970s. In October 1976, using one of the first color-coded maps, NBC’s John Chancellor depicted a white map, which then changed as states were seen as favoring one party over the other – at that time, blue for Republicans and red for Democrats. Reagan’s 1980 Republican landslide was shown in blue on NBC and CBS, but red on ABC.