I have a bright green icon at the top center of my phone which I understand to mean that something is accessing my microphone or my camera. But, I have no idea how to find out what it is. Tapping on it does nothing, and swiping it down just brings up my usual list of things such as Sound, Airplane mode, Auto Rotate, etc, etc. How do I find what it causing that icon to light up, and to turn it off?