Resources is here (in Russian, I not very good know english).
https://github.com/acterhd/hcg-legacy

I suggest to add support HCG to Krita editor.

Hey, it took me a while to see what the actual point of this color model is, but it seems that it focusses on the colorfulness instead of the tone. Am I correct?

This is a bit odd, compared to normal methods which focus more on tone than on colorfullness, because humans are more tone sensitive, but it is an interesting algorithm. I am going to implement your patches in my 3.0 branch coming week and experiment with it. (Yes, I have seen your patches on the bugtracker, but 3.0 is in full reorganisation, so I'll need to reorganise bits of it)

This seems very cool...I believe people coming from a traditional background think in this way...

let me select a colour roughly,
now add grey,
maybe its too much grey so add back some colour...
now a little bit of that colour and some of that other one...

The HSV,Lab and other models work very well but dont really get in tune with the sense that has built up over the years of mixing colours and mostly ARRIVING to a colour that happens in traditional mediums. The fun of finding a colour by mixing different paints of different intensities builds up an instinct...

Would be great to try this out when implemented.

I try to implement again. But I all forgot.
Here is legacy code (JavaScript, documenation).
https://github.com/acterhd/hcg-legacy

Probably will implemented.
https://phabricator.kde.org/D1374