You're supposed to do drawings like this in a "classical" art school, so I did one. I may or may not have pastel to draw with, but it's a lot less messy in Photoshop. I imported the shaded pencil drawing into the program and then did the coloring there.
My mother is an artist and she goes to lots of life drawing sessions. She has been doing this kind of drawing in pastel for more than thirty years and after all that time she has thousands of them piled up in her studio. All I have is a notebook and a few megabytes.