Seriously, I don’t feel as though you get rewarded for finishing camo challenges in the weapons class when you unlock platinum, it just looks bad. IW please consider reworking to make it look at least somewhat decent. Maybe go with your original idea of diamond.
If youre looking at the weapon in the "MP Lobby" patrol walk its because thats a darker environment and shinys dont bling too well there because of its lighting. A new "MP Lobby" environment is in the works with lighting that will showcase shinys much better.