50lbs MkIII - the Mk III (=50lbs) was produced in 1918 and manufactured mainly by A.O. Smith, but also by the Edward G. Budd Manufacturing Company, and by Hale and Kilburn.
The initial production has a weight of 51.5 lbs, a length of 36 in and a diameter of 6 in
It was Olive drab stenciled in black with 1 in black band at the center of gravity
Later production has a weight of 49 lbs, a length of 38 in and a diameter of 4.7 in
It may have been overall dull Yellow (= high explosive) [I am not fully sure that the yellow paint for high-explosive was adopted while this bomb was still in service - and as it was not kept among the "limited standard" war reserve, I am quite suspicious about reconstructions as on this photograph showing this bomb in overall yellow paint)
In the 1930s the denomination MkIII stopped designing the 50lbs demo bomb and from now on designed the new series of demo bombs bombs (100, 300, 600, 1100 lbs)
BTW for the best of my knowledge, the MkI was the original 50lbs Gros-Andreau produced in France for the US expeditionary force.