How do I get rid of the grey area at the bottom of page, which appears when there isn't enough content?

We want some pages on our site to not be able to scroll, so keeping this in mind the content of these pages is 'conservative'. This does mean however, that at the bottom of the page there is this grey bar, where the content has finished. It is this that I would like to make white, and thus, regardless of the screen you are viewing the site on, the whole background of the site would be a seamless white. I've attached a picture of what I'm going on about. I used the Heights template for the site. I've tried to use spacers to cover the space up until the bottom edge of the page, however this involes me manually increasing the size of these spacers, but they don't work on other devices, the page being unnecessarily long.Many Thanks for any help