how to mix colours and colour mixing systems
There are a lot of 'systems' for mixing colours out there - instructions on which colours you should use, telling you never to use black or always to use black, to use or not use complementary colours to create neutrals, to use certain brands because the mixing is all done for you and you just follow the 'rules'.
I believe that you can look at them all if you want but the only way to understand colour and colour mixing is to do it! and never ever to follow someone elses rigid painting by numbers system in your work.
It's more important to understand complementary colours and the way they make each other more vivid when placed next to each other or neutralise each other when mixed - then how to use this in a subtle way by using coloured neutrals to make a colour sing. Or understanding how to adjust a too bright colour by glazing it with a thin wash of its complementary colour.
Learn what the colours you have do, by mixing them and painting little grids like these - you'll be amazed at the variety of colours you make - and this is with just 2 colours per mix - imagine how many more if you introduce a touch of another colour and how much you'll save by not rushing out to buy the colours dictated >:>)
Look at the wonderful purples you can make from different reds and blues, from bright flower colours to subtle drabber ones - it all depends on the combination you choose and the only way to become familiar with them is to practice.
I've scanned these pages out of a very old sketchbook. I was getting to grips with what sort of varieties of of colour I could get. Some of the coloured neutrals are so useful. A dull almost purple near a yellow will make the yellow sing because it's the complementary colour - but not too loud, taking a secondary role to the yellow and allowing it to 'star'.
If you practice mixes like this you'll never have to say you struggle with greens again! you'll have a multitude of varieties of blue greens, acid yellow spring greens, ochre coloured greens. deep dark forest greens and so many more to use. :)
At university our basic palette that was suggested was Cerulean Blue, Ultramarine, Cadmium Red, Alizarin Crimson, Cadmium Yellow, Lemon Yellow,d Naples Yellow, Burnt Umber, Burnt Sienna, Viridian and White (in oils ).
This is only a beginning though - as you go along you realise that you need other colours for your own particular colour choices. I always keep those colours in as they are a good basic cool/warm combination of each primary plus the earth colours, then I add Magenta, Permanent Rose, several blues like Cobalt, Prussian and Pthalo, Aureolin yellow for its beautiful translucency, occasional colours for their gorgeousness :) like Brown Madder Alizarin in watercolour - all these extend the possibilites for you of colours you can mix.
I like to try different colours sometimes to shake things up and keep my work lively and stop me getting into a routine.
The painters I mention tend to be colourists who use colour beautifully, sometimes bright, sometimes subtle, but the colours work, like the various instruments in jazz, talking to each other :)
If colour isn't your 'thing' and tone is far more important and any green will do as long as the tone is right - feel free to ignore all this >:>)
Are you a colourist painter?