Review for Quote Colors by Alexander Ihrig
Rated 4 out of 5 stars
There is now a completely revised successor add-on that works really completely with Thunderbird 68. * and Thunderbird 78. *:
https://addons.thunderbird.net/thunderbird/addon/quotecolors/
Please note that the other / old variants of the add-on must be uninstalled!
To create your own collections, you must have a Mozilla Add-ons account.