Because a few years ago the MSM decided that Democrats would be Blue and Republicans would now be red.
In 1988 the GOP states were BLUE.
http://www.presidentelect.org/e1988.html
I think the color of red is a much better representation of what the Democratic party stands for. ;)
The color red or blue was for the challenger and incumbunt. Since Bush in 1988 was the sitting VP he was considered the incumbent.