screen bluish-white on one side, yellowish-brown on other

Hi all.

Hoping someone might be able to tell me if this is something that needs looked at by Apple.

I've had my iPad since summer and have not noticed any problems. However, recently I've been reading a lot of books on it and noticed that one side of the screen is brighter than the other (lengthwise). The darker, yellowish area is on the side with the volume button. Documents can be flipped but the shifting in color remains independent. It's not dramatic, but it is noticeable in other apps where white or light-colored pages are used.

Anyone else experience this?