Rated 5 out of 5 stars

I have used a custom version for a while, which add multiple border styles and fixes a couple of bugs.

To keep a version compatible with TB60 online, I have now released it as "BorderColors D".

https://addons.thunderbird.net/en-US/thunderbird/addon/bordercolors-d/

Rated 4 out of 5 stars

An essential tool for those using many email identities... but not too many.

A few months have passed but the issue described by Drachsi below is still a problem: the configuration dialog does not expand if you have more than a few indentities.

If that's a deal-breaker for you, you can try my experimental version fixing the issue and adding multiple frame styles.

https://bitbucket.org/dreadnaut/bordercolorsgt-dre/

This review is for a previous version of the add-on (1.0.7).