Just for clarification, is the affected area one pixel in size, or larger? If it's just one pixel then it sounds like a stuck pixel to me. There is free software available online that can perhaps fix it; JScreenFix comes to mind. I'd say you have a chance of it going away since it hasn't always been there. Take a picture of it for us so we can judge for ourselves.
is it a "spot" that shows up especially on white brighter than the rest of the screen? About the roughly the size of a medium sized star from the apple default desktop?
So this white patch is like behind the screen right? And only more obvious if you see it at an angle? I had it too, I called Apple and they replaced it with a new one.. Perfect... Maybe you should try to call Apple for replacement too..
That's definitely not a stuck pixel; it looks more like there is pressure on the screen at that point. I'm not sure if Apple will cover that but it's worth a shot. Make a Genius Bar appointment and bring it in.