Re: RBForums
The whole red (header) – blue (links) – green (visited links) clashes a bit anyway. I’d pick a single colour for all, for the best feel to the site, but others may disagree.
The whole visited links styling I personally find a bit unnecessary anyway – I’ve hardly ever found that to be useful, and then only in huge linklists which you won’t have on your forum.
Once you’ve picked a colour (could be anything really, although it should be distinctive from black so you can see the links), make a small yet distinct change to it and set it as the color for a:hover links – that way users can tell when they’re over links, otherwise it can be frustrating.
For example, on my forum (http://forums.loinhead.net/) I’m using colours #0C0066 for links normally and #060033 for links when you hover on them. Both fairly similar blues, but you can tell the difference.
There are very few colours I use for the site.
Dark blues for links; light blues in the threads listing, and #ffffee for my ‘alternate’ background – every second post, post forms and such. It’s a nice slightly-warmer-than-white colour. Using a small range like that can give you a good effect I think.
So to summarize the ramble: pick one and use it for almost everything.