One of the great features of Ubuntu’s default instant messaging application ‘Empathy’ is the support for ‘Adium Message Styles’.
These let you theme your messaging window in a variety of ways. The only draw back is that most of the ready-made Message Styles available online are made for Adium (the Mac OS X version of ‘Pidgin’) and don’t always work well in Empathy on Linux.
But Linux-made variants are available – such as this ‘Ambiance Adium Message Style’ by franksouza183.
Installation
Extract the .tar.gz archive that you downloaded above and move the folder inside to:
.local/share/adium/message-styles/
You will need to press CTRL+H to reveal hidden folders.
If the ‘adium’ and ‘message-styles’ folders aren’t already present you will need to create them (right-click > create folder)
After this just enable ‘Ambiance Message Style‘ from the ‘Themes‘ tab in Empathy’s Preferences.