My opinion - go with what looks right to you. By the time you've glossed, weathered, washed, oil pin spotted and beaten with a tire chain (okay, maybe not that last one) then the color will look entirely different anyway!
I will say the spoon color does look very close to the Olive Green on the chart, but had someone asked me what color WWII American vehicles were painted, I don't think I would have chosen that one. Seems too green to me (IMO).
Good luck!
Gary
PS> Oh, and I enjoyed your jeep build. I've got a couple of 1/48 scale Hasegawa jeeps I've been meaning to assemble, but the color for the engines has been keeping me away.