I am experimenting with a layout HERE (http://community.livejournal.com/starleticontest/)
which I have made a header and selected the background color. I found out how to center the header and all of that fun stuff, but I don't know how to change the actual blog area. I'd like most of it to be the same color as the background color, but I'm not sure how to go about doing that. Can anyone help me? Thanks so much!!

Go to Manage > Customize, then click the "Look and Feel" tab. That's where you can change the colors for the blog area. :)