I figured it out after a few minutes poking around.
You'll need some way to set "secure" settings – if you're not rooted, the easiest way is via a Tasker plugin called AutoTools. Once you've set that up, create a task with an action of "AutoTools Secure Settings", then configure it as follows (under "Custom Setting" in the AutoTools menu):
That task then toggles greyscale mode, so you can hook it up to an application context or whatever. (Switch the value to 1 if you want a task that always enables greyscale, or 2 to always disable.)
If it doesn't work, diff the output of `adb shell settings list secure` from a PC with greyscale mode enabled and disabled, and use whatever name you get there.
You'll need some way to set "secure" settings – if you're not rooted, the easiest way is via a Tasker plugin called AutoTools. Once you've set that up, create a task with an action of "AutoTools Secure Settings", then configure it as follows (under "Custom Setting" in the AutoTools menu):
That task then toggles greyscale mode, so you can hook it up to an application context or whatever. (Switch the value to 1 if you want a task that always enables greyscale, or 2 to always disable.)If it doesn't work, diff the output of `adb shell settings list secure` from a PC with greyscale mode enabled and disabled, and use whatever name you get there.