Do the colors appear in safe/troubleshoot mode (hold Option when launching TB)? Are the colors applied to tagged messages? The attached picture shows the menu on W10/91.2.

I tried your suggestion but it still doesn't display colored tags. I don't use any add-ons but it was worth a try. The colors stopped appearing the same time notification banners stopped showing up for new emails.

A bug was reported here: https://bugzilla.mozilla.org/show_bug.cgi?id=1711813

As for notifications, I understand they are partly controlled in OS X System Preferences, so you might have to reset that.

Thanks but I've been using the correct system prefs for quite a while. Perhaps I can find an earlier release of Thunderbird to try. I'll have to go through my backups....

This question has been locked because the original author has deleted their account. While you can no longer post new replies, the existing content remains available for reference.