Yellow border on the phone?

I have a sony xperia and that got a bit yellow at the top of the rim all at once

Now I have a Huawei P20 and here happens the same Why?

Do you have a picture?

http://www.directupload.net/

https://www.directupload.net/file/d/5373/mdwpj8pe_jpg.htm

And with my new phone it goes down but it is not so strong

Very bad to recognize could come from an app.

I had the problem with my Sony Xperia Tablet, as was messed with the display with the adhesive, which looked to me just as in the picture of you in the comment, these are glue spots and there must be replaced the display or the mobile phone, that is a warranty case.

Okay means the display has to be swapped but my huawei 020 I've been 6 months and there it is with me now

Warranty, make a factory setting and watch.

The display must be changed definitely, the yellow spot will be bigger, as it separates a layer in the display and thus the adhesive is visible. In my tablet it was so that the stain let it squeeze out briefly, but then came back very quickly, Sony gives 2 years warranty and Huawei also, but this is a mistake that has already existed at purchase, so this is a warranty case in both handsets where the burden of proof reversal does not apply and the dealer nachbessern.In both cases, the display can't be repaired

Here are 2 pictures of Sony Xperia smartphones exactly where the problem has occurred, and a report on the Z2 Tablet, Huawei and Sony, the displays come from the same manufacturer

https://www.galaxus.ch/de/s1/ProductRating/produktionsfehler-beim-display-bewirkt-gelbe-flecken-121483