Gimp Color Pixel Degrayscaler Tool

[denzjos]

Without a photo before / after, I don't know if I understand it, but you want to do something like 'graphic color reverse engineering'. I don't know if you used graphic tools in Gimp or a well-known plugin G'Mic-Qt to experiment with black and white/color images? In G'Mic-Qt it is also easy to use CLUTs to manipulate colors in an image/photo.

https://www.gimp-forum.net/Thread-LUT-s-...ht=lut%27s
https://www.gimp-forum.net/Thread-Diffic...ht=denzjos
https://graphicdesign.stackexchange.com/...olors-gimp