I've not seen an field jack of the color in your photo. The jackets I have seen vary in color, but I've never seen a green one. But I can tell you how to mix a more accurate one. Of course, there is more than one way to get the color you want.
The colors I've seen are in the very light and pale yellowish orange range, some would call khaki, tan, or light olive drab.
I start with olive, which I get by adding black to yellow, a warm yellow such as yellow ochre or cadmium yellow. Lighten that with lots of white. Then I add a tiny smidgen of red, such as cadmium red (and I mean tiny smidgen). If you add too much red, you get a fleshy color.
Hope that helps.