Compare it to other floor models then decide I say.
My first 6 had an obvious dark spot not too far right of the status bar time.
Returned and waited for another batch.
This one is slightly warmer at bottom and if a dark spot is there it's tucked by the battery indicator.
I compared settings menu and google.com on Safari between lots of floor models and preferred mine to about 80 percent of them. Mine looked better than a few 6+ even. So much dang variation it's hard to know what's up!
I guess you put up with what you can tolerate.
I also miss color profiles and jb. My 5 and rmini got some serious screen ugliness going on without it.
I found the difference between the sharpness of my iPad Mini (1st Gen) and iPhone 6 Plus to be HUGE compared to my iPhone 5. Even though there should already be a huge difference, I noticed a bigger difference with the 6+ for some reason. However comparing the 6+ to the 5, I found little difference