This evening I revisited my fireplace sketch from last week and had the same issue with the colors not being deep enough. Last week I applied heavy coats of pastel over the gouache in order to deepen the color. This week I am leaving it with just the gouache and the bits of pastel I used in the initial line drawing.
I like the way the figure sinks into the couch and think this composition has promise. I expect to keep at it in the next weeks.
This is a 17 X 12-inch sketch on black paper.