Stan48, Well, it's obvious to me that TB has broken some themes when run in Win7, but no one wants to admit it because they don't want to fix a problem that only affects Win7.

If the problem only happens with the add-on, I don't see how you can absolve the add-on of potentially being the problem. Even if it didn't happen prior to version 102, it is possible that changes may be needed to the add-on - future compatibility is not an absolete guarantee. Have you checked with the author?

Anyway, it looks like plenty of windows 7 related issues have been fixed in the past year, and none are currently not fixed https://mzl.la/3evbnQZ. If you feel it is fix worthy please file a bug report

I would be interested to see what occurs if you change the window7 theme.

Much of Thunderbird's colour scheme has traditionally been inherited from the current windows theme. Either as a direct mapping, or as a highlight. So changing the windows theme may see a completely different outcome. It would also make useful information to be able to identify if the issue only happens with certain windows themes.

I never saw most of the issues with Windows 7 themes because I always used the legacy windows 2000 windows theme. Boring, but functional and much faster than the windows defaults.

I changed my Windows theme to the standard Win7 theme and the problem persists. Here is screen shot showing Win 7 standard theme with Aero enabled and the dark panes in TB with a theme I use. Only the light TB theme renders the top panes with a white BG.