Comment by wahlrus

In case someone out there is looking, here's an untested recipe to lock your android in greyscale mode. It removes the menu option for changing out of greyscale (untested).

Set grayscale:

adb shell settings put secure accessibility_display_daltonizer 0 adb shell settings put secure accessibility_display_daltonizer_enabled 1

Also clear any shortcut that could toggle it:

adb shell settings put secure accessibility_shortcut_target_service "" adb shell settings put secure accessibility_button_targets ""

Disable the menu that could undo it:

adb shell pm disable-user --user 0 com.android.settings/.Settings\$AccessibilitySettingsActivity adb shell pm disable-user --user 0 com.android.settings/.Settings\$ColorAndMotionActivity

Will report back if I try it.