My Kindle 3 (which I just got yesterday
) contrast is amazing compared to my old EzReader. It's has a very light grey background with very black text. I don't even need a book light to read it with like I did with my old reader. Contrast is so good I can hold it far away and still read it cause the text looks just like a paperback but better IMO.
My old reader contrast sounds just like what you described your Kindle 3 having. Two shades of grey which isn't Pearl at all. I would defaintly return it for another one because something isn't right.