It's kinda the basic idea of using themes, styles etc that you do not go into each and every page to make a global change (Bruce can talk about this for hours
)
If you're using a custom.css (which is recommended) you can simply make your change there and it'll take effect all over the place.
Something like this:
/* This overrides the settings from the theme css file: */
.nt-body {
background-color: <YourFavoriteColorHere>;
}
No need for using !important as far as I'm aware (since custom.css is read after the other style files and background-color is not marked as important elsewhere). And - depending on your settings - don't forget to run gzipall.bat
HTH
Peter