" Mil-Spec is the specifications that the military has set for that particular component. Most times the component’s design rights are owned by the government. These designs are then made by various companies to the specs needed to sell to the Department of Defense and it’s contractors. "
In the case of how Cerakote uses the "mil-spec" designation, it is just for a color shade. "Mil-Spec Green" is a certain shade of green. There's nothing special about the chemical makeup that is outside of any other they offer. You can go add any of the three "mil-spec" colors to your cart right now and there is no disclaimer/warning/restriction when doing so.