James Gurney the author of "Dinotopia" covered Eugene Burnand's portraits that he did of World War 1 Legionnaires. His original post can be found HERE. The portraits were drawn in carbon and then colored in pastel and that combination and the realism that Eugene captured is brilliant.
I prefer to work in pencil (graphite and charcoal and some carbon) because it allows me not to just draw but to sculpt by lifting out value or drawing with an eraser. There is a lot of control with pencil but in the end one ends up with a value sketch ...gray scale. So when I saw these portraits I real took to them and wanted to add color to my drawings without getting into full blown painting or colorizing the drawing digitally.
Other than pastels there are a lot of choices these days with mixed media. There are water colors (dry or wet), Inktense (water based ink from Derwent), waxed based colored pencils, water soluble wax pastels (Derwent Artbar) and even gouache. What I ended up with, which works a lot like colored charcoal is pastels. I found that if I added a layer of fixative over the pencil drawing, I was able to add a layer of color without loosing the texture of the pencils.
Of course I have a long way to go to making this part of my preferred workflow, but there will be more to follow on this subject.
This is a direct link HERE to Eugene Burnand's online portraits. This is very good work to see and another reason I like reading James Gurney's blog as well as his Art Books.