Painting Shell holes ?

[Si Tyler]

I am currently adding shell holes to my casualty markers and one base in four of my Western Front WW1 British forces.  In dry terrain how would these be painted  I was thinking of a darker interior, Light spoil and then lighter highlight on the edge. Ideas suggestions piccies welcomed.

[Duke Speedy of Leighton]

On the very interior, a black star for shell burst on a few adds variety.
https://www.google.co.uk/search?q=shell+crater&hl=en&tbo=u&rlz=1C1GGGE_en-gbGB493GB493&tbm=isch&source=univ&sa=X&ei=PpUHUfD6PIGr0AWkjIHgBw&ved=0CDoQsAQ&biw=1024&bih=667