Light orange means it's tagged with one of your "interesting tags", white means it's not.

See [here][1] and [here][2] for some more information.


  [1]: http://blog.stackoverflow.com/2008/10/expressing-your-tag-preferences/
  [2]: https://meta.stackexchange.com/questions/19173/what-do-the-ignored-tags-and-interesting-tags-fields-on-the-user-prefs-page-do