Rumor has it that Apple may be introducing some new features in iOS 12 to help users reduce the amount of time they spend staring at their screens. One option which some research say shows benefit is the ability to turn the screen to black and white. The lack of color reduces the dopamine hit your brain gets ("ooooh, shiny!"), and can help reduce your inclination to keep interacting with it even though you're not really doing anything anymore.
You can achieve this right now by changing a simple setting in your phone. Go to Settings > General > Accessibility > Zoom. Then scroll down to where it says Zoom Filter. Change that to Grayscale. Now go back to Zoom and tap the slider next to Zoom to enable it. You may then need to double tap your screen with three fingers to go to full screen mode (otherwise it actually will zoom, in addition to turning the screen gray).
Note that this feature is persistant through a reboot. If you want to disable it, you need to go back to Settings > Genmeral > Accessibility > Zoom and turn the Zoom slider off again.
Now if we could just get Siri to talk with a Mid-Atlantic accent...