Blue to “yellow” shift is normal in all OLED phones.
And that's the reason why Apple calibrates the OLED displays to a warmer color temperatur (True Tone off).
If they calibrated it like the iPhone Xr to true white, viewing the iPhone Xs off-axis would look too extreme I guess.
They should give the customers an option though (True Tone and True White).
By the way: switch True Tone on and off a couple of times and you think your Xs screen looks white. The brain adjusts.