Shades of Brown and Grey
I vaguely remember that at school we had to do that: draw squares and then fill them with certain colours. You had to be very careful not to make a mess with your colours: not to create mud with them and not to let your paint go outside the squares. I deeply hated doing that. We did the colour wheel as well, but I was not interested in colour theory and mentally skipped the whole subject.
Now, many years later, I know that it is important to “know your colours”. I can shade with a pencil – and I want to learn to shade with colours. And in order to do that I have to know how my colours look like on the paper which I will use for the final painting. Yes, there copic colour charts on the web, but as they are a printed out version they differ from the colour you get when you put the copic on the paper.
Doing these colour charts is also something which can be done when you don’t feel like creating something. You need a ruler to draw the lines, and your copics, and the only brain challenging thing is to get the right number for the colour written down.