I went into my local Apple Store and it appears on all the iPhone 5's. That's strange. Must be something to with the layer they removed. iPhone 5's touch screen is 1 layer isn't it? Still a bit worried if I'm honest though!! But at least I found out it appears on every iPhone 5.
Just got back from the apple shop. They replaced my phone and there is no problem with the screen or green mist at the bottom of the screen. You need to call them and they will make you an appointment at the apple shop