I'm going to work on a dark theme for the Forums. It will be the exact same as the current, but with an inverted color scheme (minus the green; that will stay green). It will be similar to the ZoS TeamSpeak theme.
If there is enough interest in this, I'll try to test it and get it out before next weekend (July 11-12).
This won't be the default theme. That will remain the current to match the website. This is just an option for members to use.