It would be a nice feature to have area on the template to be the full width of the template but centered. You should be able to specify if the template is to be designed in this way. If so then you can select the background colour/texture for each of the full width areas such as the main content, module rows, banner rows etc. You can then specify the centered content width to match a specified pixel or % width or just to match the specified page width.
I have done this design quite a few times but it involves editing the index.php template and css, though it would be great to have it in the software.