Hi Lizardqing2,
I did an M1 in NATO Camo last year. If I am not mistaken it is in black, dark green and dark brown colors. I used dark green as an overall coat. The reason for this is I found it easier to cover with the two other darker colors. Then I used the dark brown and black in the same order. It would be more difficult to use dark green over black or dark brown. The color will not be right.
Unfortunately, I did not have an airbrush back then. The camo job looked fine but the paint is not so smoothly applied. I have re-done it in desert camo some months back and is now re-doing it again.
I am not sure if what I did was right but I am sure some of the guys will come along shortly.