OK here's a photo of the Pipe Major of the Black Watch showing the gilt sporran cantle, sgian, and dirk, and gold lace, insignia, and buttons on his doublet, but silver waistbelt and crossbelt hardware and plaid brooch.
Note that his pipes are silver mounted but his bagcover has gold fringe.
Seems that in the military the idea of matching metals doesn't exist, at least in the dress of pipers.