Re:
I'm guessing that you have a screen protector that covers proximity sensor. This is a well known issue. Most screen cover makers have adjusted their designs to have cutouts for the sensors
I'm on Sprint. The only options under Cellular Network are Data Roaming, Preferred Network Type, System Select and Carrier Settings. Under Carrier Settings the options are Update PRL and Update Device Config
#2 is usually from having a screen protector that doesn't have a cut-out for the proximity sensor. I had the same problem with a Spiegen glass cover until I replaced it with one with a cut-out
That looks more like a panel brightness issue than a white point calibration issue.
phonearena has some colorometer reading of the 5x and the white point is pretty much spot on: Google Nexus 5 Benchmarks
well of course that will happen when you have a phone that large (which allows a physically bigger battery) thats only pushing power to a 720p screen vs a 1080p one
i do photo editing and watch blurays on my PC so my monitor is calibrated. so is my HDTV. most browsers now support color profiles for images so calibration improves general web surfing as well.
its the only way to know that youre experiencing media the way the creator intended...