Here is what I'm pretty sure about. Underside of hood, inside of upper side panels body color. Firewall black, unlike sedans and Cab B's.
Underside of body I think is black, at least evidence pointed to that on the 55 we are restoring. The inner fender panels appeared to be black as well as undersides of fenders. I think that Cab A's got different treatment than Cab B's and sedans. A very original Cab B I know has the tan underbody and inner fender wells, but I don't remember about the fenders themselves.