Once you design for a while you get to like and know what combinations go together. You could try http://www.colorcombos.com/ which is a good starting point for color palettes.
I see. I am trying to figure out the color my readers will like based on the topic. I know I do not want pastels for anything serious or harsh colors for my personal blog...
You should check out some wordpress themes or joomla themes and get some ideas. That's probably the best way to start.
Think about the target audience and what it is you are trying to sell, you should also think about what colours work together and what doesn't. Colour blindness issues should also be researched.
colors scheme it depends on product and you may also get the color scheme from the templates sites or you may take suggestion from user what they like ...
Basically it is just a case of experimenting for me. I try to use soft colours, which is very typical of a web 2.0 trend. I also like to think about what I'm trying to promote, the colour of the site should at least be influenced by that. I stick to only one or two colours and just vary the shades to get the desired effect.
Find one nice color and put it in color wheel software, by playing with its parameters you'll find many color schemes that look good. Try them on your website to find the one that fits best.