How to choose colors for a website layout?

Given that I'm new to graphic design and I'm trying to design the homepage of my website, I can't really understand the reason why I can't make the homepage color "shine".

I'm sorry for the advertising but I'll give a list of websites that I believe have a "shining" color so you can help me in my way to do that:

http://postmarkapp.com/

http://www.taskrabbit.com/

http://rypple.com/

Those 3 sites have a background that "shines". I can't accomplish that.. everything seems light and blurry when I do it. I've tried to look for books, guides.. anything that can help me out!

Thanks!