Some Samsung phones have a great feature which turns the screen black and white by powering just the black light in the AMOLED display and shutting the red, green and blue lights off in an effort to save battery life. Technically, if your device has an AMOLED display, the same principle applies, but it may not be an inherent feature of your cell phone.
Follow these steps to download the application which operates at the GPU level, avoiding overlays, to automatically grey scale your device when the battery low signal shows on your device.

Step 1: Install Monochrome

This mobile app guarantees you automatic grey scale on any device.

Step 2: Run the ADB Command

Once the application has been installed, if you are a rooted user, all you have to do is open Monochrome, then tap "Grant" on the Superuser access request.

If you are not the rooted user, you are going to have to set up ADB on your computer, connect your device, run the app, then only can you run the following command in the command prompt window that pops up:

adb -d shell pm grant com.suyashsrijan.lowbatterymonochrome android.permission.WRITE_SECURE_SETTINGS

Step 3: Enable Monochrome

Run the Monochrome application once more, from the home page, enable the feature with the switch in the middle of the screen.

From here, the greyscale mode will automatically kick in when your device's battery hits its official "Low" threshold, which is usually at 15%.

That’s it, the grayscale mode will automatically kick in if your device's power runs below the 15% threshold. The black-and-white effect will last until you put your device on the charger, or until your battery is back above the official "Low" threshold at which point, the full color will return automatically.

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