Rated 4 out of 5 stars

Not sure what to advise. No other users have reported similar problems. Perhaps you have another add-on that conflicts with Account Colors.
=>I do not think so. The problem stay when I remove all addons .

Is the hightlighting (bold/underline) of new mail and unread messages in accounts and inboxes still working correctly in Folder Panel?
=> Yes

This review is for a previous version of the add-on (9.2).  This user has other reviews of this add-on.