I have done a 3-part step-by-step tutorial over on the Warsenal Blog that you can check out. Here's a recap of the recipes, though:
GREEN: VMC 086 Luftwaffe Camo Green, 081 Medium Olive <> 079 Golden Olive <> 020 Sunny Skin Tone <> Ivory. 089 Military Green.
STEEL: VMC 168 Black Grey, 166 Dark Grey, 160 Neutral Grey, 155 Light Grey, White. Black.
RUST: VMC 131 Orange Brown + 137 Cavalry Brown
CHIPS: VMC 151 German Camo Black Brown