The terms 'Red state' and 'Blue state' date from the aftermath of the last election. Before that the various media either switched colors every election or had blue=incumbent/red=challenger. Now the idiom overrides those proactices.
In a thread on the SDMB (link below) someone cited an article by David Brooks in the Dec 2001 Atlantic Monthly titled 'One Nation, Slightly Divisible: A Report from 'Red' and 'Blue' America' as the source of the Red/Blue state idiom.
http://boards.straightdope.com/sdmb/showthread.php?
t=282600
That article dates from a year after the election. It seems to me that the terms were in use before that, but memory is fallible...