no changes in bg color
The reason why the color is not showing is because you have this already:

body {
    background: url(images/body.png) fixed;
}


from my_elegant.css.

You have a background image already set. If you want to use a css color then you need to tweak the css for body to something like this:

body {
  background-color: #000;
}


or you can have an image background and a color at the same time:

body {
  background: #fff url(images/body.png) no-repeat center top;
}


If you are using style.css make sure that the file is properly added otherwise it could result to 404 and all the css in that file will not get applied. You can use drupal_add_css() api to add new css file or in the .info of your theme.