Unibody bottom color

I picked up a stub frame from Murray Park at Carlise and I am ready to paint it. I am probably going to use Eastwood Rust Encapsulator or Rust Bullet. This is not a show car, but might as well get it as right as possible. The frame will be painted black, but what should the bottom of unibody be painted? Is it supposed to be black, silver, or car body color? I have seen multiple methods on the forum. It matters to me now, as I want to order the correct amount of paint.
Author: Cazman