The default forum theme is set to ColorPlay Blue, which is a "dark" theme. Some people prefer a lighter theme, and at the bottom of each page in the footer there is a "change style" link that lets you select others. Each of the "Nexus" themes is lighter and should work well.
Unfortunately it appears that links in the Announcement box can be hard to see on some color variations. If that presents an issue for you, choose the "Nexus Gray" theme and those should be very readable in that color variation.
If others have tips and/or suggestions for fine-tuning of the forum, please post in this thread.