iOS 9.3 beta 2 has just been seeded to developers today. We see this version two weeks after the last release. This update brings many new features. Some of those are the ability to change the color of the screen during the night, ability to password protect notes, 3D Touch on more apps, and more. Specifically in this beta, we see the addition of Night Shift in Control Center. Before, it was a setting only in the Settings app.
To get this update, go to Settings > General > Software update > iOS 9.3 beta 2.