I am trying to center my category menu bar, and that works fine.

However, I can not seem to get the background color to match the color of the menu bar and I can not get the dashes to go away or change their color.

I have looked at the threads in here, but they are not working (maybe because I am running the new Atahualpa version)...

Usually it's just a matter of adding the necessary CSS to the CSS Inserts box. You just use Firebug to determine the selector perhaps #menu2 or something along those lines and then set border to none but you may have to add !important to the CSS to override other CSS.