Quick ,simple,and effective
Paint it completely grey and shade(similar colour to the picture).Then liberally stipple on the pale green a
Allow it to get into the shaded areas and wipe off some of the green paint and just repeat until your happy with the look.
Alternatively paint the figure green and stipple/dry brush the grey on.basically its the same method just reversing the colours.Its a simple method you'll find one or the other will fit with your painting style.its just a quick practice to see which version suits you best.
There are other more complex methods which I'm sure people will mention.This is the method I use when constructing museum display items.(its fooled many a 'grown up' over the years)
Mark.