Yeah that's the problem with mild display-related issues. What's considered a defect might be a non-issue to others.
So I managed to get my set exchanged at Causeway Point yesterday. Before opening the replacement, the CSO told me they can only do a one-time 1-1 exchange. If the replacement set is still not satisfactory I'd have to go to Google.
Luckily the replacement set is pretty much perfect. The screen is displaying an even tone as far as my eye could see. Made the effort to do the tests there and then even. Really the luck of the draw it seems.
I used the grey background that Alex posted before:
And also the "Display Tester" app in Google Playstore. Look for the grey/dark grey backgrounds and turn tge brightness down to 30%. Should set the conditions right to pick up any inconsistent colour tones.
Haha, in the photos it's probably not that obvious but in person if you look at it long enough you'll notice it. Then again, different people have different visual sensitivity towards such variances.