THIS ITEM HAS BEEN DISCONTINUED! But you can stream this DVD here: https://www.krollroberts.com/stream-videos
Using your color reference with photography, you can end up with some terrific results.
I take a photograph from my large library that shows a good example of how lights can sometimes wash out and how darks can go "black." By using one of my favorite "rules of thumb", color reference painted from life and the photograph for drawing I can get the painting to look more natural. That favorite "rule of thumb". . . "anything in shadow is darker than anything in the light."