Image may be NSFW.
Clik here to view.Thomas McMahon has knocked out some styles for the “Stylish” CSS-extension that produce brighter, better looking labels in Thunderbird.
The Stylish extension Image may be NSFW.
Clik here to view. is a user style manager: “Stylish is to CSS what Greasemonkey is to JavaScript, and unlike other methods of using user styles, most styles take effect immediately.”
When you have installed Stylish, you can follow the instructions on Thomas’s web site Image may be NSFW.
Clik here to view. to download some pre-made label styles that will turn your Thunderbird labels from this in to this:
Clik here to view.

And it’s not just a Mac-only solution as Thomas notes:
The new labels code has been tested in Thunderbird 1.5 and 2.0 on Mac and works great. It should work fine under Windows and Linux too.