The title of an inactive tab is colored when the contents of the hidden terminal change (e.g., when running top). This alerts the user that something happened while he was away.
Before upgrading to KDE applications 18.11.80, the tab title color was reset to the default color when the tab was activated. Now, after updating to 18.11.80, the title remains colored.
STEPS TO REPRODUCE
1. Start top in tab 1
2. Open tab 2
3. Tab 1's title becomes colored
4. Switch to tab 1
Tab 1's title color is reset
Tab 1's title remains colored
Linux/KDE Plasma: OpenSUSE LEAP 15.0 with KDE repositories
KDE Plasma Version: 5.14.3
KDE Frameworks Version: 5.52.0
Qt Version: 5.11.2
The same behaviour when I use command line option --tabs-from-file: all tabs except the last one keep highlighted state forever.
Looks like the bug was introduced by this merge: https://cgit.kde.org/konsole.git/commit/?id=9836d430253f40054371440a45ceed578adba5fc
As a temporary workaround you can apply this style via (Settings → Configure Konsole → TabBar → Use user-defined stylesheet)
It will disable highlight color.
*** This bug has been marked as a duplicate of bug 396689 ***