I found a 1950 semi gloss olive drab number that started as 2430, then changed to 24087 in 1956 to conform to Federal Standard 595... Wether FS595 was used through the '60's I'm not sure. Major G mentioned that standard olive drab was sometimes darkened with black to creat a deeper shade. Perhaps he can help sort this one out also.
I remember the older guys in my unit mentioning 'oiling' the paint to get it to shine on tanks, SP howitzers and such. Never did that myself though.
Ron.