Well, if you don't mind using Enamels, Humbrol 94 with some black makes a good dark green. When white is added it grays out to a decent German Field Gray. The yellow in the 94 keeps it sufficiently in the green area of gray. You can add more 94 if it loses it's green tone. With this combination you can mix it from heavy on the gray to heavy on the green as you see fit, just by juggling the ratio of colors. This way you can paint each figure with slightly different shades, even painting the blouse and the pants different shades, which adds an extra touch to your scenes. Some examples had an almost brown tone, bordering on OD. Using blue and/or red can help further adjust the color. There are many other perfectly good mixes for this color though, regardless of the brand of paint. The best thing to do is study color photos or color plates in books and look at the variations, and try to match you paint to that, and forget about pre-mixes. A pre-mixed color can be a good starting point though.