User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Firefox/68.0

Steps to reproduce:

          [Unsure this is a bug, as I have seen no report of this so far.]

Upgrade to v68.0 (64bit) using standard upgrade path on Archlinux (cli: $ sudo pacman -Syu)

Actual results:

seems to break Lighning calendar event category's colors. All colors are preserved from previous version's setup, but:

• either said colors are now opaque and cover up calendar event boxes' text),
• or calendar event boxes' text has become transparent.
  Calendar event boxes' text is fully preserved though as seen by opening box editing window by double clicking on it.

Expected results:

Lighning calendar event boxes should have continued to display text on colored background per the event category's color.

Forgot to specify that:

1. I have only two add-ons on TB: Enigmail and Lightning. Restarting with Enigmail disabled changes nothing to the event box text having disappeared.
2. I have three calendars all three are affected equally.
3. Curiously all day events are not affected, as can be seen on provided screenshot

Strange, Geoff, seen something like this before?

Does Archlinux provide a build of 68.0 and the Lightning extension?

Tb 68.0 should have Lightning 68.0 installed.

Ubuntu hasn't provided an update to 68.0 yet and I expect them to follow the update path from 60.8.0 to 60.9.0 to 68.1.0 with their corresponding Lightning versions.

I've never seen this problem using any version of Thunderbird on Ubuntu or Linux Mint.

@WaltS48:
Yes, that upgrade definitely came with Lightning 68.0 as a integral part of TB 68.0.

@JorgK:
Strange for me too. I also never saw anything like that during my many years with Ubuntu. But then Ubuntu standard update policies are much more conservative than Archlinux'.

User 'sfhowes' on the Mozilla Support Forum where I posted suggests that:
[quote]
"TB 68 is provided as a voluntary download to identify issues before 68.1 is deployed via auto-update. I don't see your problem in TB 69b4/W10, but colors and menus have presented a few issues unique to Linux in the past."
[/quote]
Only the official ArchLinux repo does not warn about anything at all, during standard update procedure. :-|

So, relying on sfhowes' comment and as a stop-gap, I'll just downgrade to TB v60.8.0 (which I still have in /var/cache/pacman/pkg/ as an element of my upgrade path) and will wait for TB v68.1. That will make me stop shouting "BUG!!" without knowing what or how and will give everyone peace during the weekend.

Will report if something else unexpected comes up. Cheers.

Roll back to TB v60.8.0. done All is back to normal.

Do you use custom theme in Thunderbird? Do you use custom styling rules using userChrome.css in your profile folder?

@StefanSitter:
I use one theme, called "Light". Sorry, I forgot to mention that. I have nothing custom at all on TB.
Also, early on, as I restarted TB 68.0 in safe mode not only was Enigmail disabled but also the "Light" theme. At that time calendar event boxes showed no change, i.e. no text was visible in them.

Related to bug 1560547?

It seems to be category colours taking over the entire box, which would be bug 1561528 and I don't know how this hasn't been noticed until now.

This is only needed on 68. The change to custom elements seems to have closed the trap I fell in.

TB 68.1 ESR / Cal 7.0:
https://hg.mozilla.org/releases/comm-esr68/rev/0d3e175d4b5aa81b6dd81913ee0c718a89642963

Same problem here on Arch Linux (Manjaro) since upgrade to TB 68.0 together with Calendar Tweaks v7.1 plugin (which is disabled now as marked incompatible with TB 68).
Not aware of this bug report, I reported it as well today
https://bugzilla.mozilla.org/show_bug.cgi?id=1580059

From the error console:

Lightning:
Exception { name: "NS_ERROR_XPC_JAVASCRIPT_ERROR_WITH_DETAILS", message: "[JavaScript Error: "this.tree is null" {file: "chrome://calendar/content/calendar-task-tree-view.js" line: 88}]'[JavaScript Error: "this.tree is null" {file: "chrome://calendar/content/calendar-task-tree-view.js" line: 88}]' when calling method: [calIOperationListener::onOperationComplete]", result: 2153185313, filename: "resource://calendar/modules/utils/calProviderUtils.jsm", lineNumber: 549, columnNumber: 0, data: XPCWrappedNative_NoHelper, stack: "notifyPureOperationComplete@resource://calendar/modules/utils/calProviderUtils.jsm:549:31\nnotifyOperationComplete@resource://calendar/modules/utils/calProviderUtils.jsm:568:18\ngetItems_/<@jar:file:///C:/SEB.NET/Daten/Anwendungsdaten/Lightning-Profile/Lg-TV-Programm/extensions/%7Be2fda1a4-762b-4020-b5ad-a41df1933103%7D.xpi!/components/calMemoryCalendar.js:496:18\nrun@resource://calendar/modules/utils/calIteratorUtils.jsm:87:33\n", location: XPCWrappedNative_NoHelper }
calProviderUtils.jsm:551

The problem is resolved for in Thunderbird 68.1.0 on Windows 32bit System

Thanks for the feedback, I forgot to mark the bug resolved.