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 seems to be an upgrade of the Gold Camouflage, as all parts of a weapon that would be covered in the synthetic black material, is instead covered with Gold, and the regular camouflaged part of the gun is camouflaged Diamond. Other Camouflages that share the trait include Bacon, Paladin, Dragon and Weaponized 115.
Diamond Camo is one of the camouflages that will apply to the iron sights, which can cause a visual distraction to some players. As well, the bright white color can make characters stand out, but doesn't stand out as significantly as that of other camouflages.
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. This is because, if the Peacekeeper was required to get Diamond for Submachine Guns, players that don't have the Revolution Map Pack would effectively not be able of obtaining Diamond Camouflage for the Submachine Guns.
Upon unlocking diamond camouflage, No Xp is awarded. However, XP is still rewarded for unlocking Gold Camouflage for the weapon that it was unlocked for at the time, as well as the Xp earned for the camouflage the player obtained to get the Gold Camouflage for that weapon, which can confuse some suspecting players.