Here's a study I did on the apple home page ran through a few filters of contrast,brightness, saturation and blur. Notice that whatever I do, the site's information hierarchy is always visible. The possible options (be it menu nav or buttons) and the currently selected option is always discernible, and mostly progress down a ladder of decreasing contrast/intensity.
The swf first starts out in grayscale, he selection of shades, make it easy to find the hierarchy of information and tell what is selected, apple in this pass uses inverted color (white on black) which is about as much contrast as possible.
The top menu is prominent but smaller as the second nav is honking big and better reflects the choices of interest to the user, and in this case the ipods are very sexy when photographed so they deserve photo menus.
As we bring in color the saturation, starts to denote where the second tier elements are, vs button in particular the accordions off to the left and right are actually dense information, so they denote which of the section is selected or not, but don't compete with the primary navs.