How can I change the colour theme?

The colour theme is defined on files with extension xrdb. You can create your own colour theme or use an existing one from tkabber/examples directory.

You can indicate the colour theme you want to use in your personal config.tcl. Simply add this line at the end of this file (if the file does not exist, create it):

option readfile $rootdir/examples/ice.xrdb userDefault

where $rootdir/examples/ice.xrdb is the route to the xrdb file.

There is a section on the Manual about modifying a theme. If your create a new theme, you can place it on your $HOME/tkabber , and then it's directory should be $HOME/.tkabber/my-theme.xrdb.