Colorzones doesn't work with gray colors

[yaitskov]

Describe the bug

Hue tab doesn't change gray color. All darktable tutorials refer to color zones feature, but it is not working with gray.
I have grey socks on picture. I have no idea how to make them pink or yellow.
The bottom line is darktable cannot change all colors.

Steps to reproduce

1. Take picture with grey areas
2. Activate color zones
3. Switch to HUE
4. Drag the curve across the whole range

Expected behavior

gray areas should change color

Logfile | Screenshot | Screencast

No response

Commit

No response

Where did you obtain darktable from?

self compiled

darktable version

4.4.2

What OS are you using?

Linux

What is the version of your OS?

ubuntu with nix

Describe your system?

nix-shell -p darktable --command darktable

nixpkgs commit aa9d4729cbc99dabacb50e3994dcefb3ea0f7447

Are you using OpenCL GPU in darktable?

None

If yes, what is the GPU card and driver?

No response

Please provide additional context if applicable. You can attach files too, but might need to rename to .txt or .zip

No response

[ralfbrown]

In the default mode of select by hue, you are selecting by (range of) color, but gray does not have a color in that computation.
Have you tried select by chroma? Raising/lowering the left edge of the graph will then adjust gray tones (but you'll need to really raise the chroma curve high to see effects of hue adjustments.

A better solution would be a masked instance of color balance rgb (global sliders in 4-way tab) or color correct (you'll probably want to move both white and black dots to the same color). For the mask, either draw a shape covering the socks or use a parametric mask selecting only near-zero chroma (C/Cz/S channel, depending on color space).