Review for Account Colors by Gordon Lack
Rated 4 out of 5 stars
Good to see it back.
Although...
>>> When restarting Thunderbird, the colors are missing. I have to reinstall the plugin every time I open Thunderbird to get the colors back.
I have this problem too - although a disable/enable also fixes it (but requires two restarts).
To create your own collections, you must have a Mozilla Add-ons account.