If you don't mind being a beta tester for a while you can now get in on the latest IM+. A whole laundry list of features has been added along with a rather nice looking dark theme available for use. SHAPE Services has pegged this as v6.2 and has taken the time to address a lot of user feedback with it as well as including a whole slew of bug fixes for notifications, contact lists, favorite lists and much more. If you're looking to give it a shot for all your instant messaging needs, you hit the source link to grab the install file just keep in mind, it is a beta.
Source: SHAPE Services