Unlock Golden Camouflage for every weapon in its category.
The Diamond Camouflage is a hidden camouflage in Call of Duty: Black Ops II multiplayer. It is unlocked for every weapon in its category after all the weapons in that category have Gold Camouflage unlocked. For example, to obtain Diamond for assault rifles, Gold must be unlocked on all assault rifles.
It appears to be combined with the Golden Camouflage, with the gold covering the parts of the weapon that the other camouflages do not cover while the diamonds are applied to the parts of the weapon that every other camouflage cover.
For the SMG Diamond Camouflages, the player doesn't need to unlock the Gold Camo for the Peacekeeper. However, if the player wants to unlock Diamond Camo for the Peacekeeper, they have to unlock the Gold Camos for all SMG, even for the Peacekeeper.