I am trying to change the background on subBlack and it wont let me. I am using an HTML Editor and whenever i preview it says Access Denied. Does anybody know what i am supposed to do??

You have to edit the style.css and upload it to your site overwriting the old one every time you want to preview a change.

Also, make sure if you want a color change that there isn't a background picture repeating, otherwise you wont see it.