i wanna change the color of my blog but don't know which is it in css.
can you please tell me which is which

Ask who ever designed the template. or use firebug.

as chrishirst says, you can use firebug
OR you can just view source and check that element's text... go to admin and edit the CSS

thanks . i don't know there's such firefox addon.
made it easier to see everything for someone who know less in coding