Yo. Here's a short article showing how to create a custom color scheme with pure black fonts n the Plasma desktop environment. All GUI, all simple, a very nice, I like, high five. https://www.dedoimedo.com/computers/plasma-breeze-brooze-black-fonts-theme-edit.html Cheers, Mrk
You can also match colors with your wallpaper if so inclined using the 'Pick Screen Color' feature. https://i.imgur.com/aU7vZ7W.png
Sorry to be ultra helpful but I haven't got a clue. No doubt the answer is buried in here somewhere but it's nothing I've had cause to configure. https://docs.kde.org/trunk5/en/kde-workspace/kcontrol/colors/index.html
Thanks for the link it's both exhaustive and exhausting (to comprehend) I find Breeze too bright and Breeze Dark too dark and so I tinker always "Saving as ..." (with a timestamp). I've mostly got things the way I like them. Unresolved: the color of the hyperlinks in the System Settings > KDE Connect page. I wonder if that is something "hard-coded" by the devs.