Hello Wally
I am currently scraping mine down to the bone and from what I can see it looks like from the factory the entire car was primed in a putty colored paint, then, using the same color as the outer body (in my case Amazon Green), the engine bay -going about half way down the transmission tunnel and the edges of the underneath, going in about 6-8 inches all around was body color. From there it looks like a two-part undercoating was applied in black. So, when looking at it from the bottom everything looks black except the inside of the rear valance which is a mixture of body color and a small bit of undercoating. It's not like the old "muscle cars" where there was body-colored overspray on the undercoating, on the BMW's it looks like the undercoating was applied after all the exterior paint was complete.
Hope that helps-
