black right margin

[Robert Neumann]

Hello,
I'm looking for a way to color the right margin of some pages in gray and 
black.
It has to be something like a thumb index described in the "page layout in 
latex" article. but actually more simple: Just a 5 mm wide plain grey area at 
the right side of the odd pages and the left side of the even pages.
Maybe there is a way of inserting a picture in the margin of fancyhdr?
Thank you
Robert