Any finish applied to RAM, that isn't RAM, would affect its radar absorbing ability. And, again, no real combat pilot wants to go into combat in a shiny jet. In real life an enemy can kill you, on a show a writer kills you. We are talking about a cartoon, so they can get away with whatever lavishness they want.
If there was any benefit, at all (even 1%), to flying a shiny combat aircraft every super power in the world would be using them.