Any self-respecting designer has to know quite a bit about the psychology of colors, and how a color or a combination of colors instinctively affects the visitor's first (and second) impression.
If you are a site owner and simply browsing this for your own website redesign and project, it can also help you determine which set of colors to go with, or at least what should be the dominant color of your website.
There are many advanced articles already written about the meaning of individual colors, but for the purpose of design, and as a quick colors reference, here is a very brief summary of colors, mostly focusing on the positive associations.