Blue metal may refer to a gun. "Blueing" is a protective metal treatment, a chemical which when applied to the steel components of a firearm, turns the metal's finish dark blue, almost black.
I'd tend to agree with The Lobster since most Naval aircraft are Gull grey with white lower surfaces. (Trainers get a lot of International Orange but I'm fairly certain POTUS wouldn't get to switch from the Big Boeing to any navy trainer I ever heard of....)