Sometimes a painting does not have the depth that I would like, and when I study it I realize there is not enough color difference between the foreground and the background.
In this painting, the background was the same color as the foreground. Because in the natural landscape there is more atmosphere between our eyes and the background, we see background colors as cooler, or with more blue tones.
By adding a grayed blue tone to the background trees, as shown in the second picture, the foreground advances and the background now recede, adding more depth to the painting.
Try it on your own painting!