For the cucumber, I washed it and the cast shadow with a bit of Cadmium Scarlet. That shadow was originally Neutral Tint only and it seems that the new wash perked things up.
What I am learning is that I must experiment. It seems that artists each have their own approach when it comes to shadowing. Ultramarine is popular, especially in mixes--Burnt Umber; Cadmium Red and Cadmium Yellow Pale; Permanent Alizarin Crimson and a bit of Cadmium Yellow. These mixes, as well as Neutral Tint, Payne's Gray, and Davy's Gray, can be a base layer for colored washes or mixed with color directly.
While reading about and testing French Ultramarine for shadowing, I began to see this pigment as very versatile as a base for greens, browns, and then some. Here is just a little bit of testing I sidetracked into. I'd like to explore these mixes further.