There is virtually nothing you can’t accomplish with these templates. In fact, I have taken elements of different templates and created hybrids to suit my needs.
Basically, you can accomplish your white background exactly as you guessed – by going through the respective CSS files for the various elements and removing what you don’t want.
As for creating certain elements that you don’t find so readily in pre-made templates, there is a fantastic module HERE[/url] that allows you do insert virtually any code you want (HTML, PHP, Javascript, etc.) to create a custom element for your site.