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If the RGB space were rendered as a cube, white, black, red, green, blue, yellow, magenta, and cyan would be corners; gray would lie at the center of the cube.

Is there a name for colors on the surface of that cube?

In simple terms, non-grayness could be quantified (with r, g, and b from [0..1]) as

abs(max(r, g, b) - .5) / .5

Here, white, black, red, orange, etc. would have a "non-grayness" of 1.

Shay
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    Usually, colours are either chromatic or achromatic (devoid of hue), black and white are somewhere on the achromatic scale thus it does not really make sense to exclude them. What would you do for 0.9999999 or 1.1? – Kel Solaar Aug 06 '19 at 09:24
  • I don't know what you mean by 0.999 or 1.1. I would treat all color values according to the above formula, so very light gray would have a non-grayness of 0.999. Nothing would have a non-grayness of 1.1. Everything on the surface of the rgb cube would have a non-grayness of 1. The sense of it is to create a color geometry from a sample (the way one might create a color wheel from a sample). I seek to interpolate by adding and subtracting compliments to fill in as much of the space as possible. This is simplified by removing one "dimension". I've chosen gray. – Shay Aug 06 '19 at 14:53
  • This sounds quite close to what https://doi.org/10.1242/jeb.204487 define as 'vividness'. Does knowing this help with what you're trying to achieve? If so, I can make this into an answer. – Droplet Oct 17 '19 at 13:22
  • @droplet, please do. – Shay Oct 19 '19 at 15:15

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A recent article in colour vision theory (an open-access version is available on bioRxiv) defined this concept as vividness.

It is based on the representation of colours in a colour solid, where each axis is one component of colour. In such solids, the origin is black and the opposite edge is white. For example, this is the colour solid of the CMYK colourspace, plotted in this StackOverflow question:

CMYK colour solid

Vivid colours are colours on the surface of this colour solid, which is exactly what you are describing in your question:

We define a measure of colour vividness, such that points on the surface are maximally vivid and the ‘grey’ centre is minimally vivid.

Droplet
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