Is the yellow just spots or the entire screen? If there is a yellowish tinge to the entire screen then it isn't a QC issue it is just a different screen manufacturer. My replacement is considerably warmer than the first but there is very little bleed. There are many posts about the warmer versus cooler screen.
The yellowish tinge is to the entire screen. It is pretty annoying when iPad is used as a second screen via air display and everything looks totally different.
Also, as i said before, it is generally not as bright as my first iPad2. i would guess around 70% of the brightness it should have.
I've just spoken to the Apple support today and they will exchange my iPad2 again.
Will take up to 2 weeks to get the replacement. Hope this one turns out to be ok!