Ok, looking at my early intel iMac, it seem feasible. There does indeed appear to be a clear outer case that's painted white on the inside. Now that I think about it, I've seen a very few black iMacs on eBay, so I just bet it works. I'd test the method on an inconspicuous location. A toothbrush works best for getting the paint off, and be sure to use at least 80% alcohol, the 70% and lower simply doesn't work. Good luck! Post pics when you get a chance.
Never Give Up. Never Surrender.