Reaching the highest prestige allows you to unlock the gold camo, but to obtain it you must complete certain challenges with the said gun. Headshots, kills or some new challenge with gun would be nice. I personally think the BO gold camo looks ugly, nothing too special, but if BO had pack-a-punched gun camo as the final camo, wow.
And I think having 1 gold gun camo per category is a good idea, but I would like the player to have the option to be able to select which gun he wants gold, and the rest of the guns' gold camo in that category get locked.