Thats really bad.Had the exact same issue. Very frustrated because I went to exchange and the New iPad Mini was WORSE than my original one purchased yesterday...... he wouldn't let me keep the original because he said the exchange had already been processed, but that I could swap it again when a new shipment came in.
2 of the associates agreed that they also saw the screen issue, we compared my original one versus the new one versus 2 on display. My original one was actually the best looking one go figure (but stood out more than the others because the yellowing was just on the bottom half of the ipad, whereas the new one I have is the WHOLE ipad screen being yellow tinted..).
Not happy and have never nit-picked before.
For this reason I hesitate.
My ultimate Test is the ifixit-site : Link
On the left and right you can see a small amount of the grey background.
If I turn the pad to landscape, the grey bar of the background next to the home button is rather green/yellow while the other is grey.