When I design sites I usually use the color wheel when choosing my colors after I have choosen my design, 2 helpful web applications I have found exteremly useful are:http://www.colorblender.com/ and http://www.colormatch.dk/ I have these 2 links bookmarked when I want to find corresponding colors. Also what was stated above that negative so very important. I have found first hand on a website that I have recently designed that even a small portion of missing negative space can affect the entire look and feel of the page.