Ciao Stefano! Yes, I am Italian, but I don't speak it. My parents (both immigrants) never taught me the language, as they wanted us to be fully immersed in English! I wish I spoke it, but alas. Anyway, I'm unfortunately not sure what you mean by "warm light against cold light." A general rule of thumb is to make the light source influence the temperature of the colors it hits. So if a cold light (eg. Overcast day) is hitting a white ball, that white will shift to a cooler hue. Then the shadow of that ball may NOT shift quite as dramatically to that cool hue, thereby making it feel warmer in comparison. Opposite for warm light. When I paint on multiply mode, I usually am picking very light colors, knowing that everything I do will darken my painting. It's very easy to crush your shadows too dark too soon, and I try to avoid that (unless that is the aesthetic of the picture itself.) I do like to lay in a solid shadow shape first, which will determine the separation of light vs shadow in my picture. Then I can use multiply mode to either add halftones to the light side (which is just a slightly darker version of the average light value) or some dark accents in the shadows. I'm happy my videos have been helping! Good luck with your work!

Beautiful piece. I really like the pops of saturated color!