Rated 3 out of 5 stars

It cannot set bg-colors of html-mails I write, right?
I would like to (isnt that the most important color?).
Setting the font family in selfwritten html-mails by account (or identity) woud be nice too.

Greets
Bibo

edit: Its all about finding the right plugin by name or description...
plugin "stationary" does the job I needed. Hard to find because its silly name for people that do not use outlook. Who uses outlook? [shaking head]

This review is for a previous version of the add-on (8.2). 

The main point of Account Colors is to allow the account owner to identify which account/identity their received and sent e-mails belong to, and when composing e-mails to know which account/identity they are being sent from. This can be done quite effectively by color coding the font/background colors in the Thunderbird user interface, without changing the styling of e-mail contents.

When composing e-mails, the background colors and font families in HTML e-mails are really for the benefit of the recipients, not for the account owner (sender). The approach taken in Accounts Colors is to color code the e-mail header, which should be sufficient to remind the sender which account the e-mail will be sent from.