That's an interesting question. I assume you're trying to match the factory shade very closely to OE. I would assume these Jeeps were all coated in the same standard medium gray primer for production reasons. Maybe someone will chime in with a solid answer, and maybe some factory production photos to back it up.
If you're doing a total repaint, I don't think it will matter. I can guarantee no one will notice a difference as long as your panels match.