Underpainting is the foundation for a successful painting and the key to underpainting is in your cartoon - lousy cartoon and you are stuck.
 

There is much spoken about "Golden Hour", but  it is still a mystery for most of us. In iLia Anossov's opinion - "Golden Hour" is when the underpainting is completed and it is time for color which all of a sudden begins to fit and  "just does make sense" with each brush stroke.