In this case, if I were to prime the hull in gray, I would leave the black on the suspension and running gear areas for shadow effect. Probably on the hull bottom also. But the hull front and rear would be in gray along with all surfaces abover the fender topsides for a uniform base color. If I were to prime. Seeing as I usually work with enamels, with their excellent adhesion qualities, and I’m not using brass or PE on the exterior, there is no absolute requirement to prime in this case. As there would be if I used that AM here and was working with some acrylics for my topside.
I could have also gone with a base color of Burnt Umber on the running gear instead of black. I really wish that Photobucket hadn’t pulled their extortion stunt, because I had some good photos of the process that I’m going to use here on older build threads.