I think the answer to this goes a bit deeper than what you or I might think is good. Basic web design theory says you want to run a 3 color, color scheme. primary and accent main colors with a 3rd highlight color.
With that in mind, then you ask what 3 colors..and the answer to that is not so simple. You can do a kick ton of research on the topic. Color theory and how it relates to the online experience is really kind of a science.
One of the things that i do is go around and look at sites that are of the same topic as the one I am developing. I specifically look at information based sites ( blogs etc ) I look at social pages and the color in the head banner. I pay real close attention to commerce sites, but break his into 2 categories. Small fry sites, and then big corporate sites. I also look at demographic information do I think the site will draw more woman, what colors do they like? will I draw more men? what colors do they like? the same goes for age break downs, what a 20 yr old likes is probably not what a 60 yr old likes.
Even after doing that I will develop a buyer profile and the people I want to target, and then seek out other sites that they may be visiting and buying from. After all of that there usually is a pattern of color choice.
Thats how I go about it anyways.