What colors to paint tree trunks?

[ErikB]

I'm trying to paint up some 28mm WWII crew-served-weapon emplacements.  I've put some branches around the pits as concealment.

I'm not sure what colors to paint the wood, though?  Bark is usually somewhat gray, not brown, like lumber.  I have no idea how to paint it.  Location is Russia or N. Europe.

Any thoughts for the insides and the outsides of the branches?  Especially in GW colors (as that's what I have, mostly, though I'm migrating to Vallejo).

Examples:
http://3.bp.blogspot.com/_zPzveb_czZk/SQpxy_KT3qI/AAAAAAAALM4/FWtl4U80h0Y/s400/Fallen+Tree.jpg

http://s0.geograph.org.uk/geophotos/01/26/22/1262200_2435d13a.jpg

http://img1.photographersdirect.com/img/13469/wm/pd2070702.jpg