Plastic Film
Sheet metal and plastic stock comes with a protective film backing which is always either clear or bright blue, sometimes both if the stock is supplied with two different surface finishes.
Most processes like laser cutting, bends and joining and riveting can be done with the plastic film left on, which is then peeled off right at the end, to preserve the, in this case, highly polished / mirrored surface and make sure the final product is scratch, dust and fingertip free.
I would imagine the bright blue is that.
Not that I think it is a new iPad shell at all.