iphone 5 screen turns gray then gets pink stripes then turns off

At random times, when I am using my iphone 5 or when it is charging, or when it is simply sitting on my couch the screen will freeze, then turn gray, then it will develop pink stripes, then it goes black and shuts down and nothing I do will turn it back on. It decides on its own when to turn back on and pretends like everything is fine, but then it happens again. In the middle of conversations, it will just die. Battery is charged, it is just totally random. I've had it for over a year so I have no warranty. What can I do?