After a couple of days of skipping work, I put in about 8 hours on the colouring today. Although a great deal has been done, I don't know if any change is even visible to the untutored eye. What remains is a number of small jobs of modeling with shadow, redrawing lines that are partly washed out, and finally adding a layer of light. Then final retouches. In other words, I won't have this done tomorrow...