Screen color looks dirty

Hi, I have two notes, I Just sold one a litlle time ago, and I have noticed that the Screen looks dirty in some parts of the Screen, like sand color and is more look in White colors like Facebook app, in one of my Galaxy this covered only half Screen and I could See like a smiley in a corner, in the other this color cover almost 90% of the Screen, something know about this? I have to say that mi phones have been of second hand.

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