I can't say for sure on the other exhausts on the market but the TiForce Exhausts with the Rainbow finish is anodized. ( I have seen other companies cans that have been painted, but lead you to believe that they are anodized.......no names need be given)
The process as I understand it works like this...
The cans are submerged into an anodizing solution and have electrodes attached to one end.
The cans are slowly lifted (longways) out of the solution, as they are lifted the current that is passed through the can is altered, different current=different color. Each can usually has slightly different colors and patterns...
The rainbow cans are a $100 option on the TiForce systems.
I really wouldn't try to polish our Rainbow can....glass cleaner and a clean rag......