Konquerer’s file listing recently looked like an (unreadable) alternating blue/white color scheme.
I think it had something to do with kwin-baghira, because MacOS does alternate item coloring. I installed and removed it, and I guess the theme must have changed it. For 3 days I was wondering what happened. Google-ing didn’t help, or maybe I was using the wrong keywords.
I found it in the end.
KDE Start > Control Center > Appearance & Themes > Theme Manager > Colors > Widget Color > Alternate Background in Lists.
I changed it to an off-white or something.