Heres something different I havnt seen here yet.

[Tombstones81]

http://www.motosport.com/motorcycle/KEITI-GAS-CAP-PAD-SUZUKI-BLUE-FLAME-2002?ride=SUZUKI;GS500E;1994

pretty good item it seems for so cheap.
Def. beats me having to repaint my gas cap.

Going to browse around a bit more and see if I can find anything other then blue and white.

[Dizzledan]

You could get ahold of some adhesive backed vinyl in any pattern you want, and just cut it to fit.
Something like this:
http://www.vinylforcricut.com/servlet/the-265/Purple-Glossy-Adhesive-Backed/Detail

Or find someone with a vinyl printer (sticker shops, t-shirts) and slip them a few bucks to run your design through their printer.

Don't you have any leftover paint?