That's correct. I can't remember if it was my Bell or one of my other helmets, but one of them specifically stated that it was absolutely not to be painted. It would compromise the structure of the helmet.
Vinyl graphics are probably the best way to go.
2010 696 ProTune Powermap programmer, EvoTech tail, Quat D Alum slip ons, Artrax wavy rotors, K&N, 14T, bar risers, G2 Throttle Tamer. Still working on swapping all of the black plastic over to carbon fiber. Oh, and no more ugly charcoal canister!