Same answer from me, @lis. Many manufacturers make a color called "olive drab", and all of them are different. I just finished a P-40B and used Mission Model Paints, and they had four or five colors of olive drab. Two of the colors were "faded" colors. My suggestion would be to get a bottle of olive drab from whatever manufacturer you want, than add white, or black, or whatever color you want to get an olive drab you like. Like my art instructor used to say: "Have fun, it's only paint".

Same from me, my friend @lis!
You can witness many shades, some of them towards green, some towards brown
Hu155 is what I use, so this is how I envisage Olive Drab.
best thing is to have a good pics of your modeling subject, so you more or less know what shade to opt for.

Silver Horse, and Fighting Rooster