Painting the Middle Mountains
These middle mountains need transition colors between the foreground and the background colors. Again, it is difficult to paint the warm color of the sunlight on September trees with the cool overtones representing the atmosphere. We landscape painters must paint the air as well as the light: the affect of the atmosphere and light on each and every surface. The more distant the surface, like the distant mountains, the more air there is to paint.
I lightened the darks on the right-hand mountain a bit and then warmed up the small area between the two middle mountains. You can see how these transition colors were necessary.
In the sunlit greens on the right-hand mountain, I have added tinges of pink to suggest autumnal colors. I painted the original plein air piece in September when the colors were just beginning to change. At that time, there were more gold-greens than oranges and rust colors.