For my beginning painting students, we do a lot of work on value study drawings, then we translate them into color. For this assignment students were given a fabric rose. They had to "render" it in pencil using all 10 values. I then took their drawings and xeroxed them, and gave them the copy. ON TOP of the xerox copy, using tempra, they did a monochromatic painting (using complements and white for the shades and tints). Their drawing essentially becomes the "underpainting".