I already made support for HCG (2.9.10), just accept changes. Reproducible: Always
Created attachment 96922 [details] HCG color model selector source
Created attachment 96924 [details] HCG color model support version 2.2
Here you can found info about HCG color model. https://github.com/acterhd/hcg-color
Created attachment 96931 [details] HCG support (latest version, from github)
Also, I fixed bug with HSV2 day ago.
The patch was apparently abandoned.