The chroma, or saturation, of a color should be carefully considered as an object transitions from light into shade. Making the shadow color too intense can create a false effect.
It’s a common mistake with beginning painters, who sometimes use pure tube colors for middle values and add white to lighten them and black to darken them.
The diagram is by Andrew Loomis, from his book Creative Illustration, still one of the best books on painting, color, and composition. Unfortunately it is out of print and expensive to obtain in its printed form.
But there’s good news: You can download a PDF copy of Creative Illustration and Loomis’s other books. They’re all well worth study.
Loomis books from Illustration Island.com
Previously on GJ: Color Obtains in the Light