The process is quite simple really. Not overly difficult to plan or execute.
The first thing I do is decide on a color scheme. I usually use one blue pigment as the base for each color - in this case Fr. Ultramarine. You can choose a cool or warm theme, a more reddish or greenish color scheme, or use more realistic color (but that takes all the fun out of it).
I mix the blue with Burnt Sienna to make a nice light grey color, that shifts and settles on the paper in such a way that not all areas are a uniform grey, but varying shades of blue and grey, with spots where the Burnt Sienna shows too. Very nice. I use this first color to define the shaded area of the tree, and the areas where branches come out, and the scarred parts of the tree. I just scrumble it on, trying to follow the curve of the trunk to give it definition, leaving lots of white space for future color.
Step 1 - First layer of color.
Crop of Step 1.
After this layer dries, I use the same mix, add a little water, pull in some more blue, and add a red - Permanent Aliz Crimson, Windsor Red...whatever fits your color scheme - to make a nice purplish color. Using this mix, I fill in some of the spaces between the base color. I just scrumble the paint on again, overlapping in some areas, leaving white spaces. I do this until it 'looks right'...shaded areas work, color follows the curve of the tree trunk. Let this layer dry.
For the third layer I use the same mix, adding more water and pulling in more blue and Burnt Sienna, but making the mixture lean much more to the blue side, and darker than the first layer. I dab this color on in the darker areas - where branches emerge, where there are scars on the bark, etc. Just look at a tree...you'll know when you've got it right.
When this layer is dry, I step back and look at the painting, seeing where it needs adjustments - more dark, more shadow, more even color, a variety of dark and light areas.
Stay tuned for the next steps!!PS I bought myself some W&N Kolinsky brushes...I love them!!!