Well Shieldtech, has finally come out with color change shields for different helmet brands. It looks like Arai and Shoei are up first with HJC and Shark coming out this Spring/Summer. Man, I've been dreaming of this! The shields are made using Transitions technology so I'm sure that they'll be good. Oh and they have a 2 year warranty. Cost is about $125-150. Not bad considering that a tinted shield for a premium helmet trips over $80.
http://www.shieldtechllc.com/index.php