white spot on screen of 5S

Dear Fellas,

I've got this spot on my screen of the iPhone 5s. It's especially visible on white background when reading text.


The above picture is not of my phone but the spot is the same (mine is even more pronounced).

I currently have my phone at the apple store (it's still under warranty). Unfortunately they fail to see an issue here and do not want to do anything with my phone and are going to return it to me.

Can you please suggest is this normal? If it's not, maybe I can point them to some refs?

Thanks in advance. Greatly appreciate your input.

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