I just finished unlocking Diamond Camo for every weapon in the game and completed a challenge. "Unlocked Diamond Camo for all Primary and Secondary weapons to unlock Diamond Camo on your combat knife." So apparently, your not supposed to get a diamond knife until all guns are gold.
Pics? You can grab a screenshot in theater mode, those little notifications do pop up in theater mode. Not saying you're lying. Just it would be nice to have a picture to post on the Camo guide or some glitches thing as well.