Review for Account Colors by Filbert
Rated 5 out of 5 stars
This is a great add-on and the loss of this feature is reason that I have reluctantly decided to move to a different email client. Just about every modern client has a way of distinguishing different accounts, I can't believe that Thunderbird doesn't support it natively and relies on add-on developers to provide it.
To create your own collections, you must have a Mozilla Add-ons account.