I've been letting my superman belt relax in the sun for the past day, and I'm really happy with the results. The sun is really flattening out the bright yellow, and turning it into a much more sublime brownish yellow, which is really what I'm after.
Hard to tell from the pic, but here's a comparison of the belt with a little over-drip of the original color urethane. Pretty cool. I'll leave it out for another day to see what happens.
As of right now, I'm very happy with the color. So it's time to pour up a bubble free belt and call that part done.