Sorry for digging through your code, but you must understand that framerate is not constant between devices. On mine, V-sync is off by default, and the game runs at probably more than a thousand frames per second, resulting in the screen flashing practically every frame. Please learn about delta time.

Also, even if we assume a typical 60 fps, the flashing still occurs 60 / 12 = 5 times every second, which can trigger epileptic seizures.