Thanks to Lyric1 for finding me the info for this skin, which is an adoption of one done by Player1 in 2014.
"The Boomerang" was a B-29 of the 501st Bomb Group, 21st Bomb Squadron, based at Guam in 1945. Like many B-29s flying low level night time missions against Japan it had its undersides painted gloss black. Unusually the 21st BS also applied a narrow band of blue grey on their aircraft, between the black and the natural metal top sides of the fuselage and nacelles.