I say it would be good to separate plane skin sections into costumizable parts. Like I said in another post, Tail, Nose, Engine, Wingtip, Wing Center, Wing Root, Middle Fuselage, etc etc.
These parts would be allowed to be set with a skin and background color. So, if I wanted a shark grin on the nose of my plane, and I want my plane to be completely black, I would set the "background color" of all the sections black and add the shark grin skin on my nose. Tadaa!
However, all textures (aka graphics or skins) must be from a library that the AH program has. No player-made and inserted skins or textures or graphics. Why? Well, if this was allowed then you would have to download every sucker's paint scheme when you fly..or disable the feature, which defeats the whole purpose. By using game set skins/graphics/skins you wont have to do that.
The whole purpose of painting your plane is the same as why WW2 squadrons had distinctive colorings... the Tuskegee Airmen had their tail painted all red, one of the fighters we have now has a blue nose, a german squadron had green hearts,etc. The point was to let others know who you were.
So you would know when you see a pink P-38 flying around.. "thats wobble!!" or "that guy's from that squadron, hes got the markings", etc, etc.
Also, players should NOT be allowed to paint OTHER players planes on their own FE. That would lead to outright cheating by having all the other planes painted bright pink or neon green so you can shoot them easier.