Okay so...which of the things in the picture or discussion is color painter?
Is it in any way related to KDE Color Picker?
I feel like of all the things you've said so far, all of which have only tried to discourage the OP to get an answer, and not actually answer their question.
I'm calling out KDE for ripping off the Windows Color Picker. Not mad at OP directly, but still, might as well go back to Windows if that's your preferred color picker.
But why would I go to Windows, if KDE has the same colour picker? Literally an argument for me staying is that the colour picker is identical, so not worth switching for the colour picker (which I really don't care about when it comes to choosing a desktop).
All I wanted was to see if anyone knew of a way to allow Firefox to use my desktop environment's colour picker. I don't care if the design is "stolen" from Windows, and I doubt Microsoft cares either. You really have picked a very obscure, and rather stupid hill to die on.
Sorry for being harsh, I'm just frustrated that the discussion here is about KDE's colour picker design, and not about customising Firefox, which is what I asked about.
It's also the truth. Brutal truth no less, they ripped off the color picker from the Win311/95 era, with no concept on an updated GUI, they just carbon copied M$..