When is the last time you saw a Web site in black and white?
Color is vital to the repertoir of your average Web designer, and yet many designers don't realize that the colors they choose may be having more of an effect than they realize. Colors are an element of design that people react to on a visceral level. Often, they don't realize they are reacting to it. For example, in the U.S. many hospitals dress their nurses in light blues and pale pinks. This is because these are calming, soothing colors, and upset patients relax a little in their presence. Once you understand your audience make up you can create a color scheme that suits them.
When choosing the colors for your site, you need to first (as always) think of your audience. Is it a global audience? Is it primarily Western? Eastern? Are they older? Younger? Male? Female? All of these things, and more can affect the color choices for your site.
Cultural Differences
Colors obtain symbolism through cultural references in the culture you grew up in. Depending upon the culture, colors can have very different meanings and actually cause problems for your site. For example, in the East, white is the color of funerals while in the West white is the color of Weddings. If you were to design a Wedding site intended for an Asian audience and you used a lot of whites, you could be disturbing the people you're trying to reach. Chart of Cultural Color Symbolism
Age Differences
Young children tend to prefer brighter, more solid colors, while adults tend to prefer more subdued colors. If you're writing to an audience of children and you're using muted pastels and shades of grey, their parents might like it, but the kids will be long gone before the page finishes loading.
Class Differences
Marketing research in the United States has shown that working class people tend to prefer colors that you can name: like blue, red, green, etc. While more highly educated classes tend to prefer colors that are more obscure: like taupe, azure, mauve, etc. This is why Walmart does their store logo in bright red.
Gender Differences
In many cultures, men tend to prefer cooler colors (blues and greens) while women tend to prefer warmer colors (reds and oranges). Western men are also more likely to be color blind and so unable to see some of the differences in color on Web pages.
Trends
Colors, like everything else in design, go through ins and outs in popularity. Black Web pages were all the rage a few years ago, and now you hardly see it at all (but it will surely come back into style as I write this). Colors also tend towards seasonality, in other words, the designs reflect the season they were built in: winter blacks, whites, and greys; spring greens and bright colors; summer yellows; fall browns and golds.