How to change background color in my Tao subtheme
It depends on the structure of the theme. If your can´t see any change after apply this, there are two possible reasons: 

body {
  color:#fff;
  background:#333;
  }



There are other elements, like divs, upon your body elemnts.
The change that you made is not reflected on your site. Check if you are working in the correct css file. If it is a .sass file, maybe it needs to compile. Other reason for that, is for the cache, try to delete by going to admin/config/development/performance


Good luck!.