Hi Marco. I used this lecture as an opportunity to move on to some simple still life. This is the first time I have painted from real life instead of pictures. Understanding color temperature and value differences really helped me make conscious choices even though the subject and background have complementary colors. I will paint more spheres as you advised and use that as the basis for color choices in more of my practices in the future.
krita has a built in gamut mask tool, using the artistic color palette and gamut mask dockers you can even make custom ones.
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.