Underpainting in digital watercolour

Here's a sneak detail from a more complex figure that's in press.
Underpainting using digital watercolour brushes is fun. Simply make your drawing layer "Multiply" mode, and use free digital watercolour brushes to paint on the layer underneath.
I think the best thing about this technique is that you can take an older drawing and jazz it up to go into a book or presentation (whereas you would have kept it black and white for the journal paper).