Borg tactical cube help

Hey, ive been building the borg ships as placeholders until the epic star trek mod is released, and ive hit a snag with the borg tactical cube. I wanna put the armour plating on it, but its gotta be silvery/grey, and the colour system means whatever piece i use comes up as green or black. Any way to mae it so an extra isnt colour coded with the ship??????

Sorry if that isnt very clear but i think it gets the jist of what i mean across lol...