Often the shadow side of the form seems to have duller chroma than the light side, but not always. It all depends on the circumstances.
In the case of this rock formation in Sedona, Arizona, the downfacing planes in the shadow were picking up warm reflected light from the ground.
The warm reflected light bouncing into the orange local color multiplied the effect, and increased the chroma. By comparison, the light side was distinctly grayer, because it was lit by both the white light of the sun and the blue light of the sky.