I've found this rather late. I purchased my first iPhone since the iPhone 7, and this time I got an iPhone 13 mini 256 GB.
The display is ---well, very yellow. Even in dark mode, the darkness takes on a color I would describe as latte maybe. Turning on True Tone is like having Night Shift on, and Night Shift is . . . well even more so. I'm past the 14 day return period. I hadn't opened it right away and had never heard of this issue before. I don't have another iPhone to compare to except my iPhone 7 which looks brighter and much more of a clean white despite its age. My Apple Watch Series 7 looks brighter and much more white than either of them. It's a perfect looking display to me. I assume having it replaced under warranty--if they even did agree to--would mean a refurbished phone? And it might not be any better. I honestly don't mind it that much, but I find it very distracting every time I look at it. I have an urge to "clean" it--it looks sort of like my display is behind a layer of smog.
Edit: I do also have an iPad to compare it to, which also is comparably very white--it's an old entry level iPad.
Edit 2: I forgot to add, I have seen this on OLEDs of pulse oximeters before, but it's as they age. I assume maybe my display was really old, but seeing these other posts, it seems that's not the issue. But that's what it looks like.
Edit 3: Playing with it more: It looks like a clean normal white color from very steep angles, and then facing it again it switches back to looking what I would describe as sometimes yellow sometimes rosy colored.