And you may ask yourself...
How do I work this?

The tabs are 24-bit PNG images, with no background color set on them. If you want the tabs to have a background color, you need to set it in a particular manner, or else their color will override the .active style (because those tab images would become opaque).

The .active style sets a background color only. The selector is placed in the Tag field of the Edit Style dialog (including the leading dot that signals it is a Class style), and the Name field is left empty. This style will be added to the tab image directly, not to the link that wraps it.

The .controls style sets a background image (a translucent white PNG image, to ghost back the tabs from the images). This background applies to the DIV that wraps the tab image, and is optional.

If you want the “normal” tabs to have a color, you should set it by creating the .controls or .controls a styles.