make it so that you can have 2 colors for the tanks and it can be toggled by activation groups or if you click the fuel tank it will say something like toggle second color. This would be cool for simulating iceing on the tanks, adding soot [more explaination down there], or a cool color change for the crafts.
[or maybe create a system to add some soot if rocket engines are ignited while falling through the atmoshere cause thats cool :)]