What Is The Color Of Shadow On Whipped Cream?

Way back in the first year of art school, I had an instructor who used to periodically gaze off into the distance and ask the class, "What is the color of shadow on white?" Nobody knew how to answer this, and I am reminded of that question as I ponder the shadow areas on the whipped cream in this painting.

Hot Fudge Sundae I, Guilty Pleasures Series, © 2020, work in progress (click on image for larger view)

There's a peachy orange light source somewhere to the upper left of the little still life, and there's also some blue light bouncing around from somewhere. Whipped cream is intrinsically slightly yellowish; think of the butterfat content. But when we try to darken yellow paint with black, it turns greenish! So I struggle with mixing in some Portland Gray or one of the umbers.