Different background for different page

Yes, that’s possible! For the default homepage, you can use this:

body.home {
  background-color: #ff0000;
}

For a specific blog post, you can use this where 5 is its post ID:

body.postid-5 {
  background-color: #00ff00;
}

And this is for a specific page and it’s the same where 5 is the page ID:

body.page-id-5 {
  background-color: #0000ff;
}