In a pinch at the track, we've simply covered the distracting labels with black racer's tape. Not the most elegant solution, but when you're traveling at speeds approaching 140mph, the last thing you need is a distraction!
For a more long-term solution, maybe a local auto parts store has black spray paint for vinyl surfaces. Just remove the visor, clean with rubbing alcohol, mask off the back side to avoid overspray, and paint the entire front side. Anyone tried this? Seems like it'd work fine.