could be different White Balance settings.
Hard to be certain.
don't jump to conclusion yet!
I set white balance auto. . gonna go nikon service centre later. .
when i put both D90 my own, and the one at my work place, taking over the same white back ground. . mine have some yellow things. . its not always at the same postion..
the D90 at my workplace one its sensor is pretty nice and its like the normal sensor u see. as for mine its yellowish. .O.O?
Its like the first image i took its on the top of my image, second on the middle , third bottom. . its across the whole imagine ( horizontally. . .)