After having been in beta for a while, the skin system is now official with the release of version 3.21.8.
There are already 23 skins to choose from. Just select the menu "Tools->Skin Selector", then click the button "Download more skins".
If you want to edit a skin to your liking, select the menu "Tools->Skin Editor".
If you create a new skin and want to share it, you can contribute it here:
http://www.coollector.com/viewforum.php?f=13