Notes on Colour

the colour wheel

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Explanation

A convenient way to visualise the range of hues is to arrange them in a colour wheel. The spectral hues are arranged in the order they appear in the spectrum and the circle is completed by placing the purple-magenta hues between violet and red.

It makes sense to begin with the six primary and secondary colours  because this gives the same six whether we are dealing with additive or subtractive colours. We can then add a tertiary hue between each of them.  (The hyphenated names of some of these tertiaries are not standard colour names—they have been added for completeness.) This arrangement ensures that complementary colours are placed opposite each other on the wheel.

These hues can be shown with greater luminance and saturation on a computer screen than has been possible on paper.  We can also show a smooth range of hues instead of the usual twelve.  

All these hues converge to grey if they are desaturated, so the colour wheel could be filled in to create a colour disc.