XChat has the ability to be themed, but not in the way many Windows users are expecting. XChat's window border and widgets are handled by GTK+ rather than by XChat directly. Instead, an XChat theme consists of the Text Events and Text Color scheme used by XChat.
Currently, there are not many places to obtain up to date Themes for XChat.
Most themes come with a colors.conf and a pevents.conf file. The color scheme is provided by colors.conf and the Text Events scheme is provided by pevents.conf. If you want only one or the other schemes, ignore the other file.
In order to install colors.conf from your theme download, you must close XChat. If you do not close XChat before copying the file, and the file previously existed, XChat will overwrite the colors.conf on close. It is therefore important that you follow the following steps:
There are two ways of installing pevents.conf, the first of which is like installing colors.conf, but the second way does not require you to restart XChat. If you are installing colors.conf as well as pevents.conf, you may find it easier to just copy pevents.conf into the Profile Directory the same time you copy colors.conf. Otherwise, you can follow these steps:
Reverting Text and Color changes
If you decide you want to go back to the default Colors and Text Events for XChat, you may simply delete the files.
XChat will use the default settings for colors and text events, but will not re-create pevents.conf and colors.conf until you either install a new theme, or manually modify the Colors or Text Events. When you have modified these, on the next clean exit, XChat will write these files once again.
As mentioned, XChat does not handle the theming of widgets (buttons and scroll bars) itself, but instead allows GTK to handle these. On Linux, simply changing the Controls in Gnome should be enough to change the controls in XChat. On KDE, if GTK-Qt is installed, the GTK-Qt theme engine will handle the widgets.
Changing the GTK+ Controls on Windows is a bit harder. There are a few sites that explain how to change the theme manually, but you may have the most luck using the GTK+ Preference Tool.
In both cases, you can specify configuration that will only apply to XChat. To do this, you will need to modify your gtkrc file, although you may need to view the source code to find out the name of a specific widget.