The skin was ported to b2evolution 2.x-3.x.
The Custom Skin was the default skin in b2evolution 1.x. It has been converted to the b2evolution skins 2.x format and enhanced with 3.x features.
It was originally designed to server as a base to be customized by bloggers. It turned out that quitr a few blogs used it "as is".
In version 3, it is possible to customize the header and menu colors directly from the admin interface (Blog settings > Skin settings)