Color theory is the practice of using the meaning behind colors to bring about a sensory experience. This practice can be applied to web design with some knowledge and thought. A carefully selected color scheme will create the mood of the website, evoke a certain emotion. That is why it is important that the color scheme used on a website is in line with the product itself, its target audience, and characteristics of a product.
Warm colors will bring about sunny emotions and are wisely used on sites that want to call to mind a feeling of happiness and joy. As a case in point, yellow became a popular color in web design in 2009 when the global economy wasn’t doing very well and companies wanted their customers to feel sunny and comfortable on their site. Cool colors are best used on professional and clean-cut sites to achieve a cool corporate look. Cool colors stir up emotions of authority, establishment, and trust.
In the end the colors used will evoke certain negative or positive emotions, and can ulteriorly affect the sales and popularity of the product you are selling on your website.
A personal example of mine are the websites of the low cost carrier airline EasyJet.com and RyanAir.com. I mostly book EasyJet when it comes to low cost airlines. Why? Simply because EasyJet seems more trustworthy the website more work, and easy to navigate, while RyanAir is very strident, too bright, which in the end looks cheap, something you do not want to be associated with your flight. So Easy jet won me as a customer partly because of their color scheme. Soft, orange/yellow color, which makes it more safe and pleasant to navigate through.
So pick your color scheme wisely when choosing the personality of the products or service your are trying to promote on your website. It really makes a difference!
Here are some links to some nice articles about color schemes.