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 Gold 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. It also very similar to other camos such as Bacon, Paladin, Dragon and Weaponized 115 in that they all (including Diamond) cover the entirety of a weapon. Magazine and all.
For the submachine gun Diamond Camouflages, the player is not required to unlock the Gold Camouflage for the Peacekeeper. However, if the player wants to unlock Diamond Camo for the Peacekeeper, they have to unlock the Gold Camouflages for all submachine guns, even for the Peacekeeper.