This Theme restores the look and feel of Thunderbird 3 on Windows 7 / Vista. It is based on the non-aero Theme of Thunderbird 5, most icons are based on the default theme of Thunderbird 3. The Theme isn't blue, so it should be compartible to all Aero Colors you might choose in Windows settings.
For the full Thundebird 3 feeling I recommend moving the toolbar back above the tabbar
.Do not disable or uninstall this theme in the add-ons section
or it will cause serious issues.