I'm not saying make your entire site yellow with black text because a zillion studies have determined this combo gets attention. In fact nobody has the magic color chart. It takes trial and error. If you have a high volume site this trial and error can happen in as fast as a day.
For example our site, chatropolis.com, has mainly a black background with white text and purple links. It also has a lot of purple in other places. If I change this main combo I get violent e-mail from my users. Upon research, purple and black make people feel sexy, and everyone likes to feel sexy.
Join forms are another story. I suggest you stray from your main site theme to get attention and perhaps induce some new feelings. We have two different join forms. A yellow background that is readable plus a light green to calm and help eject the wallet from the user. We tried red and it looked cool, but research indicated this was the quickest way to anger someone. This proved itself in an instant slowdown in sales.
There are literally more studies on color than you could read, but I suggest you read as many as you can. Having a knowledge of color and effect will make you money. In some cases it has increased our sales by 40%, in other cases it killed them by 80%.
Another mistake is thinking that because you have mastered color and effect that your job is done. I have been tweaking colors on everything from backgrounds to words for 10 years. There is always room to improve – you are never done.
A good way to explore color is to go to Alexa.com and see your competition. Examine their color schemes then hit the wayback machine and see how they improve or nosedive.
I also examine the bad sites to make sure I never do that. This can save you tons of time in trial and error and may just spark a fantastic idea that puts you on the road to greatness.
Don't underestimate color – your prospects won't underestimate it's subconscious effect!
Michael Ludwick is the owner of Chatropolis.com the Net's largest chat site for the last ten years. It is ranked #1 on rank.com and alexa.com in the chat categories.