Not so obvious under room light, but pay attention still can see the difference.
My set also has the staining issue around the fingerprint sensor.
I played around with it and it seems that the matte coating near the fingerprint sensor is not working as well as those on the rest of the back. So the sub-optimal coating will absorb the sweat/oil on my fingers and form the halo-ish stain.
I can remove the stain until it's totally not obvious under room lights by gently rubbing it with a clean tissue paper.
