At YAA they told us we have to do a finished background, middle ground and foreground in order to do a real finished painting. This is so the viewer’s eye can find a place of interest to rest by looking into the background.
YAA wasn’t a university but more like a trade school but very intense. They wanted us to learn the ways of the old masters. It’s good to give the illusion of depth in a landscape. That happens by using the tricks to create aerial perspective. You can use the same colors you have mixed for the foreground, just add some gray to make the background color.
I know some modern artists don’t like to use gray because they fear muddy colors. You can avoid muddy colors by mixing the colors on the palette with a palette knife instead of mixing the colors on the painting with a brush. Do I fear muddy colors? Hell no! Muddy colors aren’t bad if you use them right! That said, I often spend 45 minutes or so mixing my colors and adding a few drops of terpenoid in and mixing that until it’s smooth and even. It’s a slower process than modern art where you squirt the color out of the tube and dive right in with a paintbrush.
Don’t use any gray in the foreground colors. That will help separate the background trees from the foreground trees.
I used my modified fan brushes to add the texture to the background trees and dry brushed some branches into the sky. It’s a different texture than the one I made yesterday in the sedge with my palette knife. The heavier palette knife texture is in the foreground and the lighter fan brush texture is in the background.