OK, so this non-uniform colour when looking dead on at the screen has me irritated now. I can't unsee it.
Fortunately, I ordered 2 X's from different suppliers. I was going to send the second one back without even opening it, but decided to pop open the box for a comparison.
The current phone (with the non-uniform colour) is on the left. "New" phone on the right. Brightness set to the same level and True Tone on.
The difference is quite startling. In the first pic showing control centre, the left phone is slightly pinker at the top. The right phone had a uniform grey colour top to bottom.
In the second pic, the left phone almost looks lilac at the top. The right phone again is uniform, if a little darker.
There is definitely a difference in these panels. Although the right phone is darker, I much prefer the uniform colour.
I checked the serial numbers and they were made in different factories - the left in Shenzhen and the right in Zhengzhou.
I'll be sending the left phone back. If anyone wants me to do anything further comparisons before I erase it and box up for return tomorrow, please let me know and I'll be happy to help.