What's the difference between paint jobs and variants?
Solution 1:
A paint job is something you specifically create for a weapon. It uses patterns and things similar to making an emblem. They usually do not cover the entire weapon like a camo does.
Camos are obviously full skins for guns. Those are earned through headshots, challenges, and the black market.
Finally, variants. These are purely cosmetic attachments earned through the black market. They will make that particular attachment, let's use rapid fire as an example, look different than the basic attachment.
Hope this helps.