The final camo that exceeds diamond is believed to be “Dark Matter“. This info is based off the Dark Ops challenge. This is unlocked by getting diamond camo on every weapon in the game however no one in the world has done this yet – give it a few days!
Derived from /u/DidUknowiPwn‘s post, this is the entire list of Dark Ops Challenges. However, the data set I have from a <redacted> source is slightly different than his. So just to clear up any discrepancies, I will upload my own set as well.
1) Obtained – Earn Dark Matter by earning Diamond Camo on all weapons in the game.