Boy, can you open a can of worms!
I'll try to give you my best answer to this...
Confusion about the correct WW2 OD shade to paint vehicles began with the government first attempted to establish paint procurement standardization in 1950. This standardization was laid out in color list TT-C-595, the precursor of the current FS 595a/b paint chips.
During the 1920's the Corps of Engineers standardized a DARK olive drab, previously called Panama Pullman, as color #9 in their field manuals on camoflauge. This OD #9 became the standard color of all Army vehicles through WW2 and was the factory production color of all Army procured items during the war. It was also issued as a paste, to be thinned, for field re-paints.
In the field, 'lusterless' #9 OD was difficult to maintain and a semi-gloss version was adopted in 1943. However, it was factory applied only to vehicles manufactured from late 1943 onwards. It can be seen in photos of the later T23 turrets, 76mm guns, and some manlets.
When the first standardization list was published in 1950, the original #9 lusterless dark Olive Drab was no longer in use and did not appear in the publication. However the Air Corps #319 light Olive Drab remained and through a series of publication revisions, the light OD was included as a paste over chip of another darker OD in the FS595a chips. This color became color FS 34087 and is often incorrectly identified by many model paint and kit manufacturers as WW2 OD. Actually, the dark lusterless OD 34087 in the original FS595 that #319 was pasted over was a lusterless version of the semi-gloss used from 1943 onwards and would therefore be a very close match to the WW2 lusterless color.
This dark OD does not appear in current FS publications and is not produced by any paint manufacturer, and modelers have to mix their own by simulating the rare original FS 34087 chip in FS 595.
So in a nutshell, the original OD that Shermans were painted is currently NOT listed as a Federal Standard color in FS 595b and was in fact no longer used when FS numbers were first assigned in 1956. FS 34087 (from the original FS595) is about as close as you can get. The OD Green FS 34087 in FS 595a is too light. Many modelers think that the current FS 34086 (called Loam or Green Drab) color is a pretty close match to the original darker FS 34087. The choice is up to you.
Sorry for the length here...Hope this helps.