A well designed website separates content (text) from design (layout, colour, etc). Your content resides in your HTML pages and your design predominantly lives in the CSS style sheets written for the site.
Any website designer will tell you that perhaps the easiest thing to change on a website with the greatest visual impact is the colors. Most sites have a set of colors used to make up the site: background foreground, callouts, menu highlights, headings, link and visited links, header and footer, and probably much much more.
Changing the colours of a website is a simple matter of copying the style sheets and referencing the new style sheets in the site, and changing the colors in the new style sheets.
It is also relatively easy, either programmatically or using a tool, to consistently present one version of the site to each user that visits. i.e. run a color based multivariate experiment.
I have run a number of these in the past with wildly varying results; I have seen site significantly improve conversion with very little effort and I’ve also seen sites that color seems to have very little impact on. Which ever yours is, I’d urge you to try some color based multivariate testing.
Color is part of the website designer’s armory, but many designers haven’t really researched color preferences in different demographic groups and so are not properly equipped to design websites. People react to colors in an emotive way and make subliminal judgments as a result. So, once you know who your audience is, choice of color becomes veryimportant.
Who is your audience? Consider these factors:
Studies have shown that infants and young children like more primary and solid rather than textured colours. Adults tend to like more subtle colors and this effect increases with age. If you are targeting a site at children then subtle is not the order of the day, unless of course you are aiming at their parents.
Different colors may have different symbolic means within each culture. So any given color can vary dramatically in meaning depending on the cultural background of the user. One of the most iconic and extreme of these differences is the color for funerals: black in the west and white in the east. To someone from the East a Western wedding website might look rather funereal.
Some men, particularly in the west are color blind; color blindness affects about 7-10% of the population. The most prevalent type is Red-green, but there are many other types (see Wikipedia). Since colour blindness may be a cause of accessibility issues (some elements of the site may be invisible to an affected person) I would recommend running your website through a color blindness filter (such as perhaps this one) to see how a color blind person would see you site.
Colors do have cycles of popularity and varying meaning within a culture in reaction to current events or context. For example during an election period the colors of the leading parties are in the Zeitgeist. Color trends also move with the season. A red and white site at Christmas (with attending snow and other Christmas paraphernalia) means something quite different to the viewer than a red and white site in the summer with out the Christmas decorations.
This is a difficult factor to asses, as class tends to vary culturally too and education is a factor as well. However, research in the US indicates that working class users tend to prefer nameable colors like blue, red, green, etc. More educated classes have a tenancy to prefer more obscure colors. This is why brands in ‘red red’ are so popular with ubiquitous products like Coke or Virgin (UK).