Hey a while ago I also did a notan study of the first picture you shared. Maybe comparing them helps you, mine is of course also not perfect and everyone makes different decisions when doing notans. (I added 2 tones later, which is not needed at first). I think you are already making pretty good decisions and you are consistent with them. I would recommend to you to really just use 2 tones and to dont fall in the trap with pencil to shade / use more tones in the initial notan (mainly i see this in the first study). Also it think proportion can be pretty important in notans bc you can change the composition dramatically by changing the proportions of the pictures. (I see as a problem in your fourth study) Additionally I heavily recommend Sinix' video about value distillation which are pretty much notan studies:(https://www.youtube.com/watch?v=iwRa5qTnr8o&ab_channel=SinixDesign)

Thanks to this course I think I understand colour now completely, but getting a feeling for them is something entirely else. Anyway here are my tries on the exercises and happy painting everyone^^

I did 3 versions of the the exercise with a monochromatic palette. My goal was to make tham as distinct as possible while using the same palette. Next I will try my hands at the complementary palette.

I tried to paint some of the pictures from the course myself and I really like how the brushwork on the green monster turned out^^.