There are pics of an Audi A8L that is "chromed" out, since the A8L is actually an all aluminum chassis and body, they just polished the aluminum and clear-coated it; at least thats my best guess. The plastic parts are painted of course or chromed.
As for the mercedes that is chromed out, it was part of a special thing mercedes did for photo shoots, I'm sure someone else know about this. they'd park the car in italian type villages where there are a rich assortment of oranges(colors) and other deep colors(red, blue sky etc) to reflect off the car and photograph it. I think I may have some of the pics on my comp. Will look for.