I think that depends on whose NATO Green you're trying to depict, since each country would have it's own idea of what that colour should be. Tamiya has XF67 which I suspect is the U.S. equiv. From my own research on Bundeswehr colours, Hu75 came up as their colour for the pre-Flecktarn green colour, IIRC. Leave it with me for a bit, I'll come back to you...