I did place this in the style.css file and it does not seem to be eliminating the background image. I managed to make the page full width yesterday, by removing something from the style.css file.
body.page-template-page-fullwidth-php #content {
width: 900px !important; background-image: none !important;
}
body.page-template-page-fullwidth-php #content-wrapper {
background-image: none !important;
}
This would solve the need.