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 ""
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.