Here's my standard take on OD Green from WWII. It won't give you the proper color from various manufacturers, but it provides some interesting insight on the OD debate.
WWII OD Green
Confusion about the correct WWII 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 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 WWII 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 field operations the 'lusterless' no.9 color was found difficult to maintain and a semi-gloss version was adopted beginning 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 manlets. This dark semi-gloss OD was used on vehicles from then well into Vietnam.
When the first standardization list was published in 1950, the original WWII no.9 lusterless Dark Olive Drab was no longer in use and did not appear in the publication. However the AirCorps no.319 light Olive Drab, as well as several other OD shades 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 we now treasure. This color has become color FS 34087 and is often incorrectly identified by many model paint and kit manufacturers as WWII OD. Actually, the dark lusterless OD 34087 in the original FS595 that no.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 WWII 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 Pub. FS 595.
So in a nutshell, the original OD that US vehicles and tanks were painted is NOT listed as a current Federal Standard color. FS 34087 (from the original publication) is about as close as you can get. Many modelers think that the current FS 34086 (Loam) color is a pretty close match to the original darker FS 34087. The choice is up to you.