If you want to mix it from scratch then I'd recommend you start with a dark blue that you find reliably gives you a matt finish, then add in a little something like Yellow Ochre until the colour looks about right. If it's not dark enough, just add a touch of black.
If it's a little too dark then adding in a small amount of white can work, but a little of a light flesh mixture will often give a better result (slightly duller).
A flesh colour can also be a good choice for highlighting the green; for the shadows on a green this dark you really don't need anything other than black.
Einion