Colors in the Massachusetts 2012 Primary Election
On September 6 of this year Massachusetts held a primary election. As a registered voter in one party I was handed a ballot. The color did not match my expectation, so I checked the text to be sure I had the right one. In fact, the Commonwealth did offer red Democratic ballots and blue Republican ballots. When I shared this story with my very sharp best friend she regaled me with how and why my expectations were set as they were. For the record, she’s not a geogeek or any sort of geographer, just a regular, interested and interesting individual. It turns out everything she said was true.

2008 United States presidential election results by county, on a color spectrum from Democratic blue to Republican red. (Graphic by Michael Gastner http://www-personal.umich.edu/~mejn/election/, licensed under the Creative Commons Attribution 2.0 Generic.)

Early Use of Color in Voting
An early use of color on the ballots themselves dates to the 1870s in Texas. The colors were introduced to help Spanish speakers and those who could not read select the party of their choice on the ballot. The Texas State Historical Association's Handbook of Texas History Online explains that Democratic leaders called themselves the Blues, while Republicans chose to be the Reds.

Early Media Election Maps
Two-color maps in the media date back to at least 1908. That year, both the New York Times and the Washington Post published color maps exploring elections. The Times used blue for Democrats and yellow for Republicans to detail Theodore Roosevelt's 1904 electoral victory. The Post covered the 1908 campaign between William Howard Taft and William Jennings Bryan with a map coded red for Republican-leaning states, blue for Democratic-leaning states. Yellow states were "doubtful" states, and green areas depicted U.S. territories with no presidential vote.

Election Maps on TV
During the early days of maps and later electronic maps on television, between 1976 and 2004, color choices were far from standard. Some sources report that networks alternated the color of the incumbent party every four years between red and blue, the two non-white colors of the U.S. flag. Others point to NBC’s John Chancellor who asked the techs at the network to rig up a lighted map to show who won each state.  A state would glow red for Jimmy Carter, a Democrat, and blue for Gerald Ford, a Republican. That map was wildly popular, so by 1980 the three major networks had similar maps, but used different color schemes. NBC stuck with its original colors, while from 1984 CBS used the opposite symbology. In 1976, ABC used yellow and blue, but went to red for Republicans and blue for Democrats in 1980 and 1984. In 1980, yellow was set aside for John Anderson, an Independent, should he win a state. (He did not.)

By 1996, symbology was still a mix. The three major networks and CNN, plus the New York Times, used red for Republicans and blue for Democrats. Time Magazine and the Washington Post had the colors reversed.

Election 2000
The 2000 election between Bush and Gore was so close and so contested that ultimately the Supreme Court got involved. During the time of confusion, perhaps for the best, the public and news outlets spoke of “red states” and “blue states” and created a de facto standard, today’s familiar red for Republican, blue for Democrats. That year, the New York Times published its first color election map and followed the new standard. The graphics editor who made the decision for the paper had a different explanation. Archie Tse explained that “Republican” and “red” start with the letter “R.”

Sources:

• Wikipedia
• U.S. Election Atlas (republished New York Times article from 2004)