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I think the most important parameter about color is the GrayScale.

GrayScale = 0.299 * R + 0.587 * G + 0.114 * B

Whenever I need a color-space I make sure to use Grayscale as an axis.

This gives me an easy way to get "the same, but in green", and I can easily choose between background and foreground color.

I don't know if this has an official name, but for color-picking I wouldn't want to use anything else.

It might be worth noting that your Grayscale equation is the Y value in the YIQ colorspace https://en.wikipedia.org/wiki/YIQ#From_RGB_to_YIQ -- a technique similar to using the lightness value in EG HSL for picking a foreground or background color (similar to what the article does here: http://notes.neeasade.net/color-spaces.html#h-cb3c6479-7d62-...).

(I'm the author of the article)