Hmmm... Can't see it hugely clearly on my dithered remote screen, but it does seem to be a backlight consistency issue that I've come across quite often on ACD's. The inconsistency is pretty clear as some monitors are very good and what we expect in comparison to the likes of Dell: Others (many, to be honest) have been clearly to marginally not how I expect them to be.
Whether you will be able to get it replaced is a degree of how severe Applecare rates it to be. Once again, I'm not actually looking directly at this website but through a sort of intermediary which reduces the number of colours and dithers them to send it across the tubes quicker, but from what I can see of your posted picture I've had monitors worse-to-similar to that replaced (in some cases multiple times until I got one that actually was better), but others I'm still not happy with have come back as 'within nominal'.
Most of my monitors are in multimonitor configurations and I have to say that in my experience Dells - which should in theory be comparatively the acceptable face of general-purpose mediocrity as far as monitors are concerned - have more consistent panels / backlighting regardless of the neverending 'Apple is better' spewed here. Either that or many of my ACD's have fallen off the back of a truck.
Describe it as carefully as possible, and they should at least have a look at it. If you do get it replaced - as far as I know, none of the ACD's I sent away were repaired, but rather replaced with refurbs - examine it carefully when you get it, and check it out thoroughly. I've had some nightmare replacements.
