I thought I'd try this again, with a tighter crop to simplify the composition, and with a limited palette. Not so much to eliminate color, but to narrowly define it. I was back at this site yesterday, in the rain, and looking at the scene I really didn't sense a lot of color. I could see it and describe it, but it wasn't really the focus of what turned me on about this tree.
Depending on how this appears on your monitor, you may not see much more than grey, but I used a combination of the following throughout: Titanium White, Burnt Umber, Ultramarine Blue, Cadmium Yellow Light, Cadmium Orange, and a touch of Mars Black.