Originally Posted by Paper-Cut
There isn't a set list of colors that are banned. The rulebooks says any colors that interfere with the judges ability to do their job. So, in one tourney where everyone is shooting pink fill an orange gun will be allowed, but in another where the color is yellow/orange, pink is allowed but orange isn't.
This doesn't just apply to guns, masks, hoppers, tanks, jerseys, pants. It's all subjective as well since it's the head ref that decides whether your equipment will cause problems or if you're fine.
there are some colors that are specifically not allowed to be worn/not allowed to be used on gear. however, the catch all as you described is any color that may inhibit a ref from doing their job.
read the rulebook. it's in there.