The '99 is spa yellow; the '04 is Rio yellow. I just bought a yellow '04 and really like the color. It's hard to tell them apart unless you have them side by side, but the '04 shade seems to be more pearlescent and a bit brighter. Maybe less brownish. Hard to describe (and, ironically, I'm a writer!) You might want to do a search for Rio yellow. I did and found lots of comments about it.