Painting from masters

Trying to learn how to paint digitally, using a more traditional approach. In this case, I’m working with a Van Gogh’s portrait as reference. Definitivelly, the most difficult part for me is getting the light values correctly. For the cheeks, for example, I practically see the same colour. I start painting some lighter tones, but then when I have to paint the darker ones, everything seems wrong.

[Add some face values references]