If you have a disability or you only want to trigger and control Greyscale Mode which can let you save battery help use better your phone (and eyes) at night and reading tons of words (let's call it "Ebook Mode") you will have a lot of ways to do it:

✓ "Play"button inside the app
✓ "Automatic Battery Mode" which activates Greyscale Mode at a chosen battery percentage
✓ Widget from the home screen
✓ App shortcut (Android 7.1 Nougat)
✓ Notification with "Play" "Pause" and "Stop" actions

Read carefully the "Permission info" section to know how to grant the important permission SuperSu to ShadesOfGrey and enjoy your brand new accessibility function Greyscale Mode as on OnePlus 5 and other VIP phones!