Don’t get me wrong, Trillian is in my opinion the best multi-protocol IM client available for Windows right now, but the standard skin is not very pretty. Especially for users of the free versions, who can’t change the color theme, it’s quite an eyesore. But DeviantArt user Insomnautik comes to the rescue. His Trillian Astra skin Avion Pro is looking pretty sweet.
To install the skin, just download the .zip file and extract it into the skins folder in your Trillian Astra installation folder. You can then switch themes in Trillian under Preferences. Unlike older versions of Trillian you don’t need to restart the application to switch themes.