Thanks for the tutorials, they have really opened my eyes.

For this specific one, have you tried to:
1. Duplicate the background layer
2. Fill it with he canvas color
3. In your history panel, select your history brush state to the point before you have filled the canvas
4. Select ART HISTORY BRUSH, adjust the brush and paint the strokes. In Other Dynamics set opacity to pen pressure. (Check the different brush presets, they are useful).
5. When doing the strokes, the starting point, direction and brush size delivers different results (unlike when you just work with the layer mask).
5. Take regular brush and fine-tune the painting. You’ll probably have to bring it up around the edges a bit.

An useful shortcut for painting with brush is to use Alt key to get eye dropper – useful for blending colors and building gradients.

I think compared to your tutorial, this will blend blend the colors and is IMHO more realistic (probably more like an water color painting though).

(and if you want to be serious about digital painting, there is step 0 – if you do not have a Wacom tablet, get one)

http://www.photoshopsupport.com/tutorials/jf/art-history-brush-painting-effect/art-history-brush-tutorial.html

Cheers

Vaclav