Foxtrot Rangers will be the key to success in ITS missions with USAriadna - they are Camouflaged Infiltrators, and there is a Forward Observer Specialist option. You can take up to 4, and I will! Here is the new model from the starter set.
The primary color of the entire army, and certainly of this monochrome dude, is the green used on the fatigues and the armor. Here is how I painted it:
Base coat with VMC Luftwaffe Camo Green 086 (airbrush). Airbrush highlights from above with Luftwaffe + Golden Olive 079, then Golden Olive + Sunny Skintone 020, and again adding Ivory to the previous mix (if it got too "yellow" at this point, I would add back in a drop of Luftwaffe). Any "hard" parts like armor plates got a final airbrushed highlight of White.
Everything was dark-lined with Military Green 089 using a very good brush with a sharp point. Military Green was also used to glaze in shadows, and these darker parts were lined with RMS Green Liner. Edge Highlights were applied using the same mixes as the airbrush highlights, primarily the Golden Olive + Sunny Skintone + Ivory + a drop of Luftwaffe mix.
To keep things consistent, I mixed small batches of the mixed highlight colors in spare eyedropper bottles.