The skull "Hydro dipping film" which one there are loads.
Save your money get a regular two tone and replace / paint / dip it when you have a defence. The dipping is gonna cost you as much as the gun, depending on what you buy, might as well spend that oney to get something you really like not something you can put up with.
As for the legalities, its probably illegal, but either way do you want to be the one who ends up in court to find out?