Under I have pasted in Promotheus ANJ`s picture + notes on saturated gradients.Picture +text = copyright Promotheus ANJ.
"The gradients between the shadow and light is not just an in-between color of the shadow color and light color. If the shadow and light is just blended, it will look very lifeless. If you look at pictures you will see that the gradients is saturated. It's especially easy to notice if you remove that saturation".
My question is - how would this relate to the ball? It is obvious how it relates to a syllinder.It helps the form turn. As can be seen in the pic. Maybe this is derived form the information in Loomis book succsful illustration where I`ve heard its written that the full light is less saturated than the middle light. This was also discussed inPP1.