Here's a little blurb from an article on techtv regarding the paint job

Quote:
After the color is applied, a clear varnish is put on to protect your new device from scratches and the like.


The article can be found here:
http://www.g4techtv.com/screensavers/features/50241/Review_Apple_iMac_G5.html

Looks like is might be an exterior paint job.