The problem with "touching up" only one part of a box is that you won't be able to match the metal flake that came from the factory. You can color-match the shade of silver, but you can't control the amount and size of the flakes inside the paint. Every company uses different flakes, so it's never going to match perfectly.
So IMO, if a box needs touch-up, you might as well repaint the whole thing in a totally different color, IMO. This is your chance to improve the box. The vast majority of boxes would look better in a different color. Be bold, be different.