Gary,
The WWII applications seem to defy description. The field-applied method varied from straight line to big waves. The 315th applied the paint with a spray set-up, so they got the soft line somewhat right. Some airplanes have the black farther up the fuselage than others, and some painters actually masked off the lower frames on the nose enclosure and sprayed them as well. Others simply masked off the entire nosebowl and left the frames NMF. Same goes for the ring cowls on the engines.
If my reference source is right, Renton factory-applied--or depot-applied--black to a bunch of aircraft. Oddly enough, a few photos I've seen show serial numbers quite near to FIFI with this paint, so I guess it's feasible she was delivered with black belly?
Here is what I'm led to believe is a factory-applied job on a B-29A landing at Boeing field:
Here are a couple of shots of Milt Johnson's Second Air Force B-29A trainer taken at Great Bend AAF around Christmas of 1945. Note how shiny that black is, and the paint line is entirely different from the Boeing Field picture:
And here is my all-time favorite B-29B photo (for now!), taken by Harold E. Groenthal on Guam. 315th Wing, 331st Bombardment Group (VH), field applied camouflage:
Scott