I've been working on color theory and value.. but I could still use a lot of advice! The only books, dvds, or sites I've found on the subject are Practical Light and Color with Jeremy Vickery, Color Theory: The Mechanics of Color with Richard Keyes, and This ImagineFX tutorial. I also feel like these Force books (Force: Dynamic Life Drawing for Animators, Force: Character Design from Life Drawing) have helped me loads in just generally drawing.
Here is Daenerys Targaryen from Game of Thrones.. I personally can't see the likeness at this point, but I've had others say it does look like her. lol Also recorded the entire process and upload it to youtube.