It's its under 1 joule it's an imitation of a firearm so needs to be painted so as not to be confused with real firearm unless you have a defence Nader VCRA.
But and here's the crazy bit, if its more powerful but less than 6ftlbs it's not an imitation firearm...because its a real firearm and we are allowed airpisrols under 6ftlbs.
Crazy but don't complain or they might stop us having them as well