If you are like me [I'm a bit of a scrooge and have only invested in the three primary colours plus black so far].
I would like to have a ready stock of colours made up so I can mix them according to a recipe [loosely] or use alone.
Here is a website to learn how to do that. I love it and now have a stock of colours ready and waiting, whenever I want them.
You can either use them as they are or mix them together to get more colours. If you make up a stock of black in the same way you can add these in tiny amounts to get shades. How good is that? :)