iPad screen color calibration - old vs new

I recently bought a second iPad and was surprised to discover how different the color calibration is. My original iPad from three months ago has very crisp whites, I guess towards being blue, but the new iPad has very yellowish whites. To be honest, if I didn't have the two side by side both look okay, but when I put the new one next to the original, the new one to my eye looks terrible. Now for the new iPad I did ask to see another one and it was exactly the same. I'm assuming that the screens are from different suppliers, but I'm still surprised at the difference in calibration, even taking this into account. So, I'm wondering if Apple have deliberately changed the calibration of iPad screens. Anyone else experienced such differences?