For those who like dark borders and title-bars, this theme, released yesterday, I believe, is worth checking out.
It is specifically for Windows 8.1 update 1.
It will not work on any other version of Windows.
It solves the following bugs that other themes have:
1. The text background colour of the title bar does not change when you change the titlebar background colour.
2. The context menu in the Start Screen works properly.
You will, of course need to install a theme patcher before using it.
I use UXStyle, since it does not alter any Windows files.