iPhone 6+ screen turned purple, faded to black, now iPhone won't turn on

This morning, I was going through Instagram and all of the sudden my iPhone 6 plus glitched and the screen kind of turned purple. Then, it started slowly fading to black and I have not been able to turn it on or use it since. I've tried holding the power button down and holding both the home and power button down but nothing happens.

Just now, I've tried connecting it to my MacBook Air. It opened iTunes and recognized that I connected an iPhone, but I have been unable to do anything because iTunes is making me enter my passcode... on my iPhone. Obviously I am unable to do this. My iPhone has previously had problems where it would randomly restart, but that has been it.

Any help is much appreciated!!