This one has changed quite a bit since I posted the first version. Something about it was bugging me; the horse didn’t seem to have as much energy as I wanted, so I kept playing with the color. Then after really studying my reference photo and comparing it to my painting, I realized that the horse’s chest was too broad, and the angles of his front legs were wrong, especially his left front leg. It needed to be much more slanted. So I drew the legs over, using black paint for the outline, filling the leg shape with blue, which was the underpainting for the horse, then painted in the negative space around his legs with red (a mixture of naphthol red and vermilion), which is the underpainting color for the grassy areas ... et voilà, THAT’s the energy I was looking for! I got it back by correcting the angle of the legs.
Here’s the painting with the old legs superimposed on it, and then the corrected version, so you can see the difference.
Check back again tomorrow for more work on this!