This painting by Clark Hulings (1922-2011) shows a whitewashed wall in shadow. The ground is orange-colored dirt. Warm light reflected from that dirt shines up on the wall, especially on the bottom half.
The blue of the open sky floods across the top of the wall, interrupted by a slash of direct sunlight.
This painting illustrates the principle: “On a sunny day, vertical surfaces in shadow usually receive two sources of illumination: warm ground light and blue sky light.”
The cool and warm sources alternate on the uneven surface, depending on whether the planes of the wall face a little downward or upward. Hulings achieves this effect by applying warm and cool tones over a darker mid-tone with a painting knife.
Clark Hulings website
Wikipedia on Clark Hulings
This point is explained in Color and Light: A Guide for the Realist Painter
Hulings book: Timeless Beauty: Pursuing Life's Textures
Hulings: A Gallery of Paintings