So with my very grey-looking tree, I used some dry-brushed in some FolkArt Mushroom and then Barn Wood on top. I also washed in some more black, FolkArt Coffee Bean and FolkArt Fawn.
Still not happy. Now it just looked like a stone tree.
So I looked up a few trees that were actually used as gallows trees. Running this one picture through Reaper's Power Pallete (such an awesome tool) - yes, the greys are there, like the Ashen Grey I used - but it's juxtaposed with strips of olive and mossy greens.
Meanwhile running this picture of another in Texas the undercoat has very dark browns - like in a brown liner or walnut brown. But where the light hits is a dark muted greyish-purple, which Reaper notes it as Dark Elf Shadow and Dusky Skin Shadow.
My painting buddy and I were talking about the color palette trees. During the winter season, I see a lot of leafless trees on my walks. We both observed that - despite all your crayon drawings as kid to the contrary - most trees are not brown. Or at least not the bark of most tree (pine trees excepted). The outermost layer of bark (called "cork") is usually grey. Couple layers under that is secondary phelloderm, which is more brown.
Eventually I got it right or close to right. Its all about washes. Rich brown washes in the underside shadows, mossy green washes on the side hidden from the sun, and some final very wet black wash to end. A little dove grey highlights at the top, but otherwise its all in the wash.
Here's the backside...