Ever since v0.4 there is Theme support in PBCS.

You can create your own Themes if you like.

Go to the themes directory and use the 'pbcs_theme.php' as template.
The themes consist of a table colors array and an images array.

Add and entry in the THEMES.list file in the following format:
<theme_file.php> <Theme description>

example for pbcs_theme.php:
pbcs_theme.php PBCS Default

In v0.4 there are two complete PBCS themes, namely:
pbcs_theme.php and xinit_theme.php

The rest of the themes are copied from SquirrelMail (www.squirrelmail.org)
and extendend correctly within the theme.php file.