This exercise is designed to investigate the mixing of colours in a colour wheel. Using your own colours rather than those any website or book might recommend is where the real value lies. There’s no theory that can replace the experience of how your tubes mix together – it’s a tangible, real world experience.
Here’s how I recommend proceeding:
Firstly, become comfortable with the basics of the colour wheel. Most art books have something sensible to say about this and a good summary is contained in the first couple of sections on this website: http://www.colormatters.com/color-and-design/basic-color-theory
Secondly, watch the following video clip. The video may be a little rough in places, however it summarizes my approach to colour and mixing:
Now see if you can develop a colour wheel along similar lines – repeat the video, pausing as you go. My approach is to follow a variation of a palette based on 2 versions of each primary, in “warm” and “cool” versions. This aids more predictable colour mixing.
When you have finished following the video, prove to yourself that you can de-colour each of the primaries by mixing in a little of the complement: what tonal colour does each give?
Finally, take one of your tonal colours: burnt or raw sienna, yellow oxide/ochre, burnt or raw umber…it’s not really important which. Put out a small squirt and then see if you can replicate the same colour by mixing just the primaries together…as you see, that same target tone will appear…perhaps a little magically!
Give yourself a well earned pat on the back!