[miffel]

It's setting your phone/screen to stop displaying color, instead just showing everything in greyscale. I believe that on Android you can currently set something like a bedtime for your phone that will stop displaying colors at a certain time, and if you have any time limits for apps then during the last minute before you run out of time it will turn grey too.

[MrGinkgo]

Interesting! I'll have to give this a try and see what effect it has on my social media usage. My new years resolution is to use it only 30 minutes a day at max