Rated 3 out of 5 stars

Not a bug! It's not the fault of the add on; it's my own thickheadedness. I can't figure out how to save the colors I choose when I select them in the extensions tab. Sorry for posting in the reviews, but I'm not seeing any way to reach the developer either. My copy of Thunderbird is up to date. I'm on a Mac (also up to date). Any useful suggestions will be appreciated! Thanks

Hello Pete! Someone else brought up this issue a while ago, and a solution was to close the color picker after choosing each color. Another person had to create a new TB profile, so the cause is not clear.

Have a look at this discussion, feel free to add there
https://github.com/dreadnaut/bordercolors-d/issues/30

Links to code and bug tracker are at the bottom of the "About this add-on" description, here:
https://addons.thunderbird.net/en-US/thunderbird/addon/bordercolors-d/#addon-description

Let me know if they are not visible enough, I can look for a better place.