I couldn't find this is the native Settings anywhere, but I did find the Greyscale Mode toggle by creating a Nova shortcut for Activities under Settings called 'Settings$PowerSavingsModeSettings2014Activity'. I imagine that should save battery power as it puts the S4 screen in a greyscale mode theme. So, now is there any way to create a direct intent or something to get to the Greyscale Mode page directly, or maybe even a Tasker intent to toggle it on/off?