I've noticed that whenever I open up a webpage, or any application for that matter that has a lot of white on the screen, the entire page seems to be dim.. Does your phone do this? Open up Google, and then press the menu button. You'll notice when the menu pops up the page illuminates, but when you go back to focus on the main page, it'll get darker again... whites look terrible on this screen...
I read somewhere that it's a battery saving feature, and Samsung, who made the AMOLED panel, has a feature to turn it off in their settings on Windows Phones. Nokia doesn't have the option so you're forced into it.
It's mainly because an all white (or mostly white even) screen on an AMOLED display is a huge battery drain.
This is a well known problem for AMOLED screens. They don't reproduce whites with accuracy and are generally oversaturated in color. If you are looking for true whites go the SLCD route as on the Titan. The upside is colors pop but its a constant trade-off against whites and creating the hues you see on your screen.