there are some threads about DYI painting iBooks and Macbooks, but I believe the iMac is hard to disassemble, if it's like the white macbooks you should take off the white paint and paint yourself afterwards. Since it's a desktop I doubt there are films etc.
It takes about 10 minutes or less to get the front off of the intel imacs. There are connections for the isight camera and microphone to be careful with. Once off you could more easily apply a film. I think the people that do graphics for outdoor signs have a film type material that might work and best of all I am sure they can precision cut it for you. You could paint it but would need to find a paint that is made for pvc/polycarbonate material and allow sufficient cure time before putting it back together. I have seen people get good results doing this on a dell mini9 which has a lid made out of colored pvc.
Replacement bezels are available, the parts supply company I bought my replacement imac hdd temperature cable from, had them brand new for around $125 usd. You know, in case you bork it up.
If you do decide to do it posts some pics and lets us know how it went.
found the tangerine macbook thread disassemble it, take the paint off and either spray it or like that guy did with the tangerine macbook put in the oven