Hi Claudio,
My first instinct is to agree that you most likely got a defective screen as a replacement. Since I am a Pixel user as well (6 Pro) I tend to notice Pixel-related questions that come up and I see a disturbing trend in that there seem to be far more defective screens on the Pixel products than on any other phone I've noted. My personal opinion is that I think Google has a quality control issue with their replacement parts.
If you bought the screen from iFixit, then you can be assured that a) it is a genuine Google part, and b) it has a lifetime warranty and can be returned for warranty replacement.
If I were in your position, I think I would want to try plugging in the original screen (assuming it's functional enough to be of any use) and verifying that the yellow tint is not present. That would pretty much point the finger of blame squarely on the new screen and you can go about asking for a replacement with a clear conscience. Otherwise you would do well to get in touch with the iFixit Store personnel (email at support@ifixit.com is best), or wherever you bought your replacement and discuss the situation with them.
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