Why not just use the default threaded view of email. Simple, clear to see and the thread is all together. Although I would recommend the traditional table view of the mail list pane over the new table view as it somehow manages to flatten the threads into some sort of flat thing that is exceedingly difficult to in the user interface.

That image looks like Thunderbird version 2. While version 2 had message threading it did not really come into it's own until version 3.

If you want to apply tag colours to backgrounds in the message list, there is an add-on:

https://addons.thunderbird.net/en-US/thunderbird/addon/tag-toolbar/

It's not compatible with 144, but the same effect can be achieved with userChrome.css.