Thanks! I used Vallejo Model Color Black Green (70980) as the base.
After that I'm not entirely sure but I think it was:
Badab Black wash
Black Green
Black Green with a bit of Vallejo Game Color Camouflage Green (72031) mixed in for a warm highlight.
I think Black Green is a great colour, very close to the old Citadel (Coat d'Arms) Dark Angels Green.