Add padding to make the background colour extend beyond the original object itself. e.g. the following displays the enclosed paragraphs in a blue box that extends 1em beyond the paragraphs and has an extra 0.5em of transparent margin top and bottom:
Code:
<div style="background-color:blue; padding:1em; margin:0.5em 0;">
<p> ... </p>
<p> ... </p>
</div>
The box doesn't interfere with the flow of the text, it will break between pages as normal.