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I've sat for hours with my iPad 4 next to my iPad 3 (swapping places often). In the dark, in the light, at all different angles.

The only difference I notice is the 4 has a warmer/pinker screen while the 3 has a colder/bluer screen. It's slight, but enough to notice.
 
I've sat for hours with my iPad 4 next to my iPad 3 (swapping places often). In the dark, in the light, at all different angles.

The only difference I notice is the 4 has a warmer/pinker screen while the 3 has a colder/bluer screen. It's slight, but enough to notice.

By warmer do you mean yellow-tinted? Mine has enough of a yellow tint that pure white background pages such as one finds in the Kindle reading app are far from the reference white one might expect.
 
Do you also have the pink hue?

Also my iPhone 5 has it, and my iPod touch 4 gen & ipad 3 and 4 to..

http://imageshack.us/photo/my-images/839/iphone51y.jpg

By warmer do you mean yellow-tinted? Mine has enough of a yellow tint that pure white background pages such as one finds in the Kindle reading app are far from the reference white one might expect.
 
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