The three primary colours are Red, yellow and blue. When mixing any two primary colours you will create a secondary colour namely Orange, green and mauve. Every primary colour has an opposite that is a secondary colour, which is its complimentary.
Rule #2: To increase the intensity add one up towards yellow plus white.
These rules are the most important to understand when it comes to mixing colours. Let us have a look at examples of what is said above. Take Red for example if we add its opposite colour Green you will see the intensity (brightness, purity, etc.) of Red reduces. Green can only be added to the point where Red becomes Neutral grey, beyond this point the identity of the colour changes to Green.