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

<p>See <a href="http://blog.stackoverflow.com/2008/10/expressing-your-tag-preferences/" rel="nofollow">here</a> and <a href="http://meta.stackexchange.com/questions/19173/what-do-the-ignored-tags-and-interesting-tags-fields-on-the-user-prefs-page-do">here</a> for some more information.</p>