I did this 2 hour studies to practice. My goal with this exercise was to paint correct values, with complementary colors, without an underpaint. I always struggle with digital because I depend too much in layer modes. Usually I do a black & white underpaint and color with a new layer on top in either color mode or multiply.  I know a lot of artist do this and get amazing results, but personally I get too frustrated with this workflow, I want to be able to paint with less layers. I will appreciate if you can critique these paintings, if you have any tips to improve, it will be helpful.  Thank you for your time, and I hope you have a good day :)