IIRC, it was the election of 1992.
Your memory might be better than mine, as you've probably watched more elections via television than I have.
From the first election I recall seeing on television, red signified the Democrats, blue the Republicans.
It seemed that way for the longest time, until 2000.
That year, I got greatly confused when Alphonse Capote Gore was inexplicably blue, and George Bush red.
I've heard it's because the mainstream media of course understands the implication of "red," and wishing to deflect any nefarious hints about the Democrats, switched them; that it was a subliminal thing, so the public wouldn't think of the Democrats negatively.