Not all 56th FG "bubbletops" had NMF undersides, and there are photos showing camouflaged aircraft with "grey" undersides, which might be either Neutral Gray, or RAF Medium Sea Grey, as RAF paints were sometime used "in the field" when US paints were not available.
I still think the photo above shows a "grey" underside, with the bare patch where the pylon was in bare metal.
Regarding the possible tail-plane stripe, it's difficult to tell, but the area marked seems to me to be rather too far outboard.