Hello Darkness My Old Friend...
I guess you did not read the introduction note: If you switch to dark mode you have to reset custom colours once. The reason is that custom colours will always override default ones, but custom colours for the light theme are obviously not valid for dark themes. That should solve the issue, please report back...
WCM 26.02 Dark Mode Issues (?)
* updated README for RPi
* created tag Release_26_02
- updated ReadMe files on SF.net
Feature requests, bug fixes, dark mode, HiDPI and WoA64
Feature requests, bug fixes, security and new compiler