The base color of the Flying Heritage Collection’s M55 self-propelled gun is quite different from the Shermans and Jeeps of World War II.
After the war, the basic color of armor trended darker and glossier than what you see in the 1940s. Glossier paint, let’s call it “eggshell,” helped keep the machines cleaner. While the move to darker paints is less clear.
Some military men relate that commanders asked their maintenance personnel to add black to the standard olive drab paints to make the vehicles darker. Perhaps the darker paint was thought to blend in better in the forested regions of Germany. After all, a betting man would have said that the next big armor battles were bound to take place there.
With careful research of photos and documents, a few color swaths, and conversations with the staff at the Lewis Army Museum at Joint Base Lewis-McChord, the results can be seen here.