A Confluence or Linchpin intranet can be quite massive with tens of thousands of pages. Naturally, not all of them will be part of your navigation menu. But probably the most important spaces are part of the menu. In order to help users to orient themselves, you will see an optical hint as to which top level menu item the current page belongs to.
In future releases there will be more convenient ways to define such an optical hint; for now we implemented css classes. Using those you can style this optical hint differently, if you don't like the standard styling.