Green Flickering during FaceTime and flashing light

Whenever I FaceTime I notice that my little screen where I can see myself, flickers with green every time I FaceTime! I just want to know why it does this and it gets very annoying. And also one day I was putting my phone (while on ft) in front of the mirror and through the mirror and my small screen where I see myself it just flashes white but when I look at it myself it doesn't appear. Even when I'm off FaceTime and on the camera app. It still flashes! (Hope this makes sense) trying to upload the photo but don't know if it's posting :(