Step-by-step instructions for turning on grayscale
Note for Samsung phones: The instructions are Settings > Accessibility > Grayscale
Minimum Android 5.0 required for the following instructions
Step 1) Turn on developer mode. To turn on developer mode, go to Open Settings > System > About phone.
Then find "build number" (usually one of the last items in the list) and repeatedly click it 7 times. You should see a bubble that pops up indicating developer mode is now active.
Step 2) Back in the system menu, there is now developer options button. Inside developer options, scroll down to the hardware accelerated rendering section, find "simulate color space" to turn on grayscale