Under 15 U.S.C. 76, "imitation guns" are supposed to have blaze orange tips, but there's nothing as of yet (on the Fed level) regarding real firearms. IIRC, CA and NY had laws in the works making it a felony to paint muzzles certain colors, but I'm not sure if they went anywhere.
Basically "the guy" (as with most know it all's hanging around KHSC), doesn't know crap about the law. You're free to paint your firearm whatever color you want without fear of arrest. Personally, I'd avoid blaze orange for obvious reasons, but to each their own.