Change Background Image per page

Try using this:

{
background-color: #e0e0e0 !important;
}

For each page you’ll need a different class. Eg.

.page-id-1 {
    background-color: #ccc;
}
.page-id-2 {
    background-color: #ddd;
}
.page-id-2 {
    background-color: #eee;
}