I have tried to make a picture converting a screen shot of the setup in 3D of my daughter’s phone
Yellowish only appears depending on the angle, so is not a problem, but there are signs of some kind of “dust” or “burned” areas, that apparently do not appear in mine that was a new Verizon device(see below, sorry for the low quality)
Edit: I wonder about the possible origin of those dishomogeneities. I had noted in my daughters before and believed to be a consequence of some not perfect repair (I have found also a fragment of plastic in the SIM tray that at the beginning created me some issues). But after seeing your case and (maybe) some other mention over the forum, I’m starting to consider if they could be result of some internal overheating at the border; this could even become something to expect over time on new devices with use; I hope this is not the case, even for Lumepad (that usually in my case becomes very hot e.g. if playing Asphalt). If the origin is hence a deterioration of the DLB, it would be interesting to know if there is anything we can do to preserve the DLB of those display, or if the origin is elsewhere.