Order of assembly? From a bare shell

What is wrong with using white underneath there on a white car?

I don't remember that all Mopars were black underneath.
I do know that Mopar people have a conniption fit if you paint under the hood black unless it's a black car.
i like them both ways, but like my car that still has most of the original undercoating, my choice is old black or newer black. body color and you need to get under there and clean to keep it looking good