I recently answered a question regarding icons. At the link I mention there are three methods. The 'Chosen solution' was selected by that user as their option, but you can choose whatever you want. You can manually set colours on a per folder basis in Thunderbird or create a method to auto create colours or get the old icons back. Image examples below - yes I know it's a dark theme but I'm sure you get the picture. Read info here: https://support.mozilla.org/en-US/questions/1309818

The instructions were for a Windows OS user, so as you use a MAC there is only a slight difference. Menu app icon > Preferences (not Options) and Help > Troubleshooting Information click on 'Open folder' button - Note: Under Application Basics section, about 8th down 'Profile Folder' - I think it will say 'Open Finder' in a MAC.

A developer states "Very likely he has a dark LW-theme applied. The fix should be hopefully in the next release."

To Toad-Hall: Are there any options that are less risky? To Wayne Mery: Does that mean I have to wait at least a few weeks before an option can be had?

To fix the highlight colors, start in safe mode (hold Option when launching TB). Do the colors of selections and icons look correct? If they do, the layout may have to be reset, or hardware acceleration may need to be changed. Report your results here.

If, in addition, you wish to restore folder pane icons with solid colors, there are a few ways, the simplest being the Phoenity Icons add-on.

Do the colors of selections and icons look correct? If they do, the layout may have to be reset, or hardware acceleration may need to be changed. Report your results here.

Yes, the colors have reset in Safe Mode. How do I make those changes permanent when opening normally?

Launch in safe mode, check 'Reset toolbars & controls', 'Make changes & restart'. Does it look OK now in normal mode?

HUZZAAAAH! I have my Thunderbird back!!

I have similar problem with automatically upgrade to 78. version. When pass pointer over unread email line in mail list, it highlights to a white background and then you can't read the line. If already read email or selected (so background is blue) it can be read. I went back to 68.12.1 version and all is ok. Somebody messed the 78. basic config for windows (I use both 32 and 64 same problem).

78.4.3 fixed the invisible (dumb stupid bug) weird problem that 78.4.2 had. I also fixed dumb icons, with at least better ones you can see. The this extension: Phoenity Icons which will only get better (imho) with allow automatic updates for this extension.