I am quite familiar with the concepts of colour theory from many years of painting, however I have read that it is different with polymer clay. Using Magenta, Lemon Yellow and Turquoise as my primary colours (as they are meant to create purer colours with polymer clay, than the traditional red, yellow and blue in paints), I mixed equal proportions to make the secondary and tertiary colours, resulting in the twelve standard colours on a Colour Wheel. I cut a square from each of the twelve colours as my starting point and when baked, laid them out as a central column.
To the left I made squares mixing white with each of the colours in turn, in the following proportions: 25% white + 75% colour, 50% white + 50% colour, 75% white + 25% colour and also 87.5% white + 12.5% colour. To the right, I made squares mixing black with each of the colours in turn, in the following proportions: 25% black + 75% colour, 50% black + 50% colour, 75% black + 25% colour and also 87.5% black + 12.5% colour.
Here is a photo of the finished results. It shows quite clearly (as I read after I had started this exercise) that you do not need to add as much black to change a colour as you do white. There is nothing like learning the hard way!
I had planned to repeat this exercise, using the more traditional red, yellow and blue primary colours, to compare the difference and also to show the variations you get when adding brown or grey and pearl or translucent clay to the twelve colours. I will do this at some stage but as it takes so long to mix all the samples, cut and bake and uses up quite a lot of clay, it will have to be resumed at a later date.