What's causing the discoloration? Most of the navigation bar is black (off). So why is there such an obvious discoloration when that part of the screen actually gets used?
You could look at it as the rest of the screen burning in, and the nav-bar and notification bar being the only two parts that don't. Because the rest of the screen is actually being used, the blue OLEDs dim a little bit, whilst the unused ones in the nav-bar area are just about good as new. That means that the nav-bar area will be tinted blue because the blue OLEDs are healthier than in the rest of the screen.
I think there may be an 'initial drop-off' in the brightness of blue OLEDs, as well. So it starts at 100, and quickly drops off as you use the phone to a point where it decreases at a much slower rate from there on in.
That actually gives me an idea for an app which could fix this, which would show a blue image at the top and bottom over where the nav-bar and notification bar are, and then have the rest of the screen as pure black. If you left that on for long enough, perhaps you could dim the blue OLEDs in those areas enough to reduce the disparity between the different areas of the screen. Of course, if you do
do that, and it somehow screws up your phone, we'll just pretend I didn't say this.
By the way, blue has the shortest lifespan of any OLED colour. Sort of funny, then, that Google would choose blue as their colour scheme from ICS going forward - though I suppose blue is the coolest colour (in every sense of the word).
Oh, and it isn't a screen fault. I have no idea how other people have managed to not have their screens burn in around the nav-bar (watching a hell of a lot of movies, perhaps?), but it's standard OLED behaviour and one of their most well-known drawbacks. It could be that I'm right about my initial drop-off idea, and they have just watched enough movies/full-screen stuff to have the blue OLEDs around the nav-bar go through that drop off as well.