Actually, it’s not connected to pages directly, TVs are associated to Templates and Templates are associated to a given document.
If you need to change the background-color of the entire site, you could use the
CSS as MODx document method and use a chunk you would make editable for your users (permissions have been upgraded and you can control this since 0.9.6). Then you insert your {{background-color}} chunk in your CSS document.
Of course it’s not as flexible as using a TV, but you can’t use TV with the CSS as document method, since CSS document have a blank template (therefore you can’t associate a template to your TV).
There are certainly other ways, either js (using mootools or jQuery to change the background-color, since you can manipulate CSS selectors with them... maybe create a background-color TV, and then add a js call in the header with the TV as parameter) or php (a little snippet I guess could work).
