Although my initial drawing was good, I really did mess up the proportions when blocking in the big shapes. Things are looking much better now. However, there seems to be an overall dullness. Not sure why. Maybe there's no contrast between warm lights versus cool shadows etc.
Maybe I could try some washes. I've never done that before, and I'm not really sure how to do that. I also don't know if I really want to start using that as a technique to "fix" poor initial color judgements. Hmmm. This will need some thought.