mx4 settings

I set up the body background all white, but still, I cant find a way to make the borders color different from the page color. Everything just goes white. The thing is, I want to be able to edit the borders color, leave the page blank and insert the header image – which seems to be blocked by the colors, like the original mx4 http://www.mx4.info/weblog/

This is how mine looks right now http://diego.crube.net

Can anyone help me out?