Thank you for your help! ubuntu-desktop was indeed not installed, probably because I removed one of the dependent packages at one time because I did not want it.
-- You received this bug notification because you are a member of Ubuntu Desktop Bugs, which is subscribed to gnome-control-center in Ubuntu. https://bugs.launchpad.net/bugs/1926088 Title: Appearance: Window colors selection does not work To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/gnome-control-center/+bug/1926088/+subscriptions -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs
