I thought the reason why we don't allow custom skins is so that people will modify them to gain an unfair advantage. What people will do is change the skin for purple players to yellow, red players to blue, etc.
If we have a uniform that people aren't allowed to change that gets placed over the model, (like helmets are placed over the skin in Minecraft) that should work.
If you're playing DM, the uniform will be removed from the model, allowing you to see the whole skin because I don't really see a purpose for the PB uniform in DM other than to make the player look like a paintball player.