I am reading the book "Catching Light in Your Paintings" by Charles Sovek. He describes the value range used in paintings to catch sunlight. He reminds us that black in shadow is only the half step between black and dark grey and black in light is medium grey. White in shadow, because of all of the reflected light from the sky and from the surrounding light-struck objects lightens to a a half step between light and medium grey. All the other colors fall in line with these guidelines.
This is a small sketch thinking about these relationships.