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Tips: How to set your phone to monochromatic
Iphone - Use your search function to find "Color Filters". Turn on color filters and select greyscale.
Android - First you need to enable Developer Mode. Open Settings, System, About Phone. Tap on Build Number 8 times.
Second, Go back to System and then into the new Developer Options menu. Open Simulate Color Space and chose Monochromacy.
Other versions of Android might have this under Accessibility if you do not find it here.