Have you ever tried to design a good looking page and found that it is really difficult to choose good color combinations?
There are some guidelines that can help you to increase your good looking tries:
http://www.colorsontheweb.com/combiningcolors.asp
With that information it is easier to come up with better color combinations. However, calculating the triad of a color is not something that you want to calculate by hand. There are some specialized programs that do this, but Adobe has a cool website that let you do this using the browser:
http://kuler.adobe.com
You can take a look at the cool color editor here:
Also, the website has a lot of great color combinations, you can search combinations by name, rate combinations, comment them, etc.