The 4-primary color wheel shows how we see colour, how our eyes and brains work.
Ewald Hering wasn't the first to identify four primary colours instead of three. Before him, Leonardo da Vinci (1452-1519) had already classified yellow, blue, red & green as a basic set of 'simple' colours. However, Leonardo didn't arrange these colours in a circular model. The 4-primary colour wheel is Hering's invention. Using a Bias Colour Wheel to understand the elements of colour, makes mixing bright or subdued colours easy to understand, much more easily than the traditional " warm" or "cool" colour wheel process.
A workbook and lessons, on line and in class, to learn how to use this method has been created and will be available soon. Contact me if you'd like to be informed.