Hi Matt, all of the UI is made up of bitmap files and settings in CSS files, which are under the \ui sub-folder inside of the main installation folder.

So it is possible to change the appearance by making a new skin that has different bitmaps and CSS settings.

But it is a fair amount of work to do so, it's not like there is a checkbox somewhere that you just click to "make things dark".

For an example check out this previous thread:
http://moi3d.com/forum/index.php?webtag=MOI&msg=1521.1

- Michael