Color and Web Design

99designs.com/

From the blog at 99designs.com, I found a good summarizing article about selecting the appropriate colors for your web design project.

Color communicates. A lot of that communication is on an emotional level because color choices can influence a visitor. 

Warm colors can have an energetic effect but used alone they can also over-stimulate, so they are frequently mixed with cool and neutral colors for balance.
Red—active, emotional, passionate, strength, love, intensity
Pink—sweet, romantic, playful, warm, compassionate, soft
Orange—warm, enthusiastic, success, determination, friendly
Yellow—youthful, lively, energetic, fresh, optimistic

The cool colors have a calming effect on the viewer, and that is why they are the most common colors used on websites.
Green—fresh, calm, relaxed, trust, peaceful, hopeful, healing
Blue—comfort, clarity, calm, trust, integrity, loyalty, reliability
Purple—glamour, power, nostalgic, luxury, ambition, spiritual

There are also neutral colors that when mixed with warm or cool colors can tone down primary colors and provide balance in web design.
Gray—respect, wisdom, patience, modern, longevity, intelligent
Black—powerful, bold, serious, elegant, luxurious, dramatic, formal
Brown—friendships, earth, home, outdoors, credibility, simplicity, endurance

There are also trends and traditions such as red and orange used for restaurants, banks and financial institutions using blue, and luxury products packaged in black. And color theory goes much further than the 3 groups above. If you really want to go deeper, look into three commonly accepted structures for a color scheme: triadic, complementary and analogue colors.