It seems that most admins take inspiration from the terminal interfaces used to communicate the story throughout the trilogy as a representation of the layout/font/colors that the Pfhor and Lh'owon used on all their computer systems. This results in Jjaro designs like
FBO and terminal-y interfaces like
MBO the story page.
The Pfhorums originally ran a theme called "Hardwired." It was probably chosen to be dark because
FBO was dark. Also, PHP board themes are
really ugly, so I probably just used the first dark theme that didn't look like crap. Of course, then it was customized with a cool logo and header and smileys and all that junk.
The new Pfhorums theme was chosen to be similar to "Hardwired." Again, PHP board themes are
really ugly so I picked the best theme I could find and then worked to correct the most glaring design crimes while adding some Marathon touches.
Simplici7y is not dark, and
does not include any red or green highlights. It's probably the least "Marathon" inspired design in the community. So, that adds to variety, but it doesn't really help you find designs that are both marathon inspired and different.
I think that the website for
Rubicon X is one of the most stunning websites in the community. It's up to you to decide how Marathon inspired you think it is.