Unfortunately I have lost the name of the lady who wrote the book coining the name ‘octanics‘ for me, but i liked it and it stuck.
By mixing colours that are close together on the colour wheel you will get the brightest colours.
The further they are away from each other on the colour wheel the greyer or more neutral will be the result.
Basically all the colours on a colour wheel will lean towards (are biased) towards one or other primary.
A typical example of the blue side of the triangle is Ultramarine blue leans towards red, another way to describe it would be to say it is a warmer blue, than say Pthalo blue which leans more towards green and yellow and could be decribed as being cooler.
On the red side Alizarin Crimson is cooler or leans more towards blue than Cadmium Red which is slighly yellower.
The results are thus:
Cadmium red is far from Pthalo Blue on the wheel = CR+Pth B = Greyish/Neutral Purple
Alizarin Crimson is close to Ultramarine Blue = AC + UMB = Bright = OCTANIC PURPLE!
Understanding Colour Mixing
From a very interesting article on Jacksons website “The basic idea to have in your head when mixing colours is that the more pigments that are added to the mix the darker and duller it becomes because each pigment absorbs light, so what is reflected to our eye becomes less and less. Mixing paint is called ‘subtractive mixing’ for this reason. Green pigment absorbs all colour but green, which it reflects back. Red absorbs all colour but red, which it reflects back. If you mix green and red, the green and red are both absorbed so neither is reflected back and you have a dark neutral colour. You can use this to dull down a colour that is too bright by adding a bit of a complementary colour (opposite on the colour wheel) a little at a time.”