Switching it on is easy. Just enable it is the same way you adjust your brightness on the phone. display’s brightness level.
Here’s how to do it: Settings —> Display & Brightness —>Blue Light Reduction. From there, switch it on and then adjust your custom colour temperature according to your needs.
Automatically decide when the colors will change. You can do so by either enabling it from Sunset to Sunrise, or a personal schedule for when you feel you need it.
Is this a new mind blowing feature? Not really – f.lux has already done it for PC and jailbroken iPhones, but still, it’s nice to have a native setting that does it for you. Do remember to switch it off when watching or taking photos as it might skew your perception of the shots taken though!