@hudson155,
gun metal grey is a HEX or Munsell color number. It was from the family that gave us "Battleship Grey"
Munsell numbers cover as many colors as we can define. I think that there are tens of "Gun Metal greay" shades on the Munsell liswt. Google up "Munsell color+ Gun Metal Grey" and you will get an alpha numeric tag. A color described by some given name like gun metal is actually vague to those in color engineering (or in mining, a careful and repeatable description of the rocks being mined)