Heh, <img src="smileys/smiley4.gif" border="0" align="middle" /> that's exactly what I'm working on now. Each level has it's own color, so each frame corresponds to the level number. it doesn't even require another variable.
Actually, I already have a transparent PNG gradient with texture stretching to fit. The color layered behind it will make it look like different backgrounds each level with very little extra download time.