you can get diamond camo and thats by getting gold on everything in that class

It's diamond, but people say it is gold with diamonds on it, others say it is platinum with diamonds on it.

It can be difficult to get, but persevere if you want to be one of the few to hack diamond guns!

Right now, I am going for diamond specials, the specials are the; ballistic knife, assault shield, crossbow and combat knife.
What you have to do is get gold on all those guns which is 100-300 kills with each plus more challenges. After you get the last weapon gold, say the assault shield, you will get the gold for it and the diamond camo for the other special weapons.

This applies to every gun class such as assault rifles, sub machine guns etc.

Hope this helps!

So does that mean I need to get say my an-94 double prestige and prestige get gold camo for knife also on the 2nd weapon?

to get the an94 gold ( like you used in the example )
you need to get EVERY assault rifle to gold camo.

then every assault rifle will have diamond camo.

Ok I have the diamond combat knife it is a goals knife with mostly diamonds the only bit that is gold on the knife is the handle the whole thing is covered in diamonds