Honoria's Suggestion: S used red to show the muscles. Scott is not happy with this color rendering. In my opinion, the color itself is not a problem. The core issue of creating volume or mass for the muscles is a range of values. You may achieve value contrast using black and white and you can achieve contrast using color with black and white added.
The first step S can try in a redo is apply white to highlight masses of the muscle drawings.
Here is a pattern of values in drawings of the muscles of the torso by artist Eric Lindsey that might give a feeling for lighting the forms. Note the torso study using red.
Learning to use color is a great challenge but it is not necessary to this class. I do encourage trying out all kinds of drawing tools and techniques during the anatomical study phase of our class. You will learn the bones and muscles even if your drawing experiment does not live up to your personal goals for each drawing. However, by experimenting with new art supplies and techniques you will have learned not only the bones and muscles but also the strengths and weaknesses of the media you try out. So I support drawings that have solid anatomical information that may not be wonderful drawings in and of themselves because they will contribute to better life drawings at the end of the term.