From this story about the police arresting some kids with blacked-out pellet guns:
"These toy guns look realistic to us as police officers, especially at night, and especially when the orange muzzles have been blackened out. We can't tell the difference. And if we come across somebody who's carrying a firearm like that, they are going to be challenged."
So...if I buy a real assault rifle and paint an orange muzzle on it, I can carry it around anywhere and you'll assume it's a fake? Score!