Average margins of victory in the five presidential elections from 1992 to 2008
R >20
R 10–20
R 3–10
R <3 b="" d="" to="">3>
D 3–10
D 10–20
D >20
Origins of the color scheme
Before the 2000 presidential election, the traditional color-coding scheme was "Blue for Republican, Red for Democrat,"[2] in line with historical European associations (red was used for left-leaning parties).[3] Traditional political mapmakers, at least throughout the 20th century, have used blue to represent the modern-day Republicans, and the Federalists who preceded them. Perhaps this was a holdover from the days of the Civil War when the predominantly Republican North was “Blue”.[2]
Even earlier, in the 1888 presidential election, Grover Cleveland and Benjamin Harrison used maps that coded blue for the Republicans, the color Cleveland perceived to represent the Union and "Lincoln's Party", and red for the Democrats.[4] The parties themselves had no official colors, with candidates variously using either or both of the national color palette of red and blue (white being unsuitable for printed materials). Time magazine assigned red to the Democrats and blue to the Republicans in its election graphics in every election from 1988 to 2000. The Washington Post's election graphics for the 2000 election were Republican-blue, Democrat-red.[3]
There was one historical use, associated with boss rule, of blue for Democrats and red for Republicans: in the late 19th century and early 20th century, Texas county election boards used color-coding to help Spanish speakers and illiterates identify the parties;[5] however, this system was not applied consistently in Texas and was not followed up anywhere else. In 1908, The New York Times printed a special color map, using blue for Democrats and yellow for Republicans, to detail Theodore Roosevelt's 1904 electoral victory.[6] That same year, a color supplement included with a July issue of the Washington Post used red for Republican-leaning states, blue for Democratic-leaning states, yellow for "doubtful" states, and green for territories, which had no presidential vote.[7]
http://en.wikipedia.org/wiki/Red_states_and_blue_states