I originally bought a white iPad air, but later exchanged it with a black one. The black one seems to be yellowish on one side, and bluish on the other. I didn't scrutinize the white iPad that closely, but I don't remember it having any such issues. I went back to the apple store today to exchange the black, but they were out of new 128gb iPads. They asked if I wanted an opened one, I said I'll wait.
I tested the demo units they had, and all seemed to have some form of yellow tint/fading.
On a side note, tomorrow was to be the last day I could return the iPad (14 days) but they extended the return period on all items purchased since Nov 1 until Jan 7th. It's their holdays return policy.
If they refuse, you can return it for a full refund and purchase another one.
Also, you don't need a Genius Bar appointment for exchanging a recently bought item (within return period.) I just talked to a random employee when I had mine exchanged, they didn't even check the box.