Does it ever go to any other colours -- like green? Because the white colour is created by mixing red + green + blue light, if it's showing purple, it's possible the green element of the diode has failed so it's only mixing red + blue. That would explain it working for recording (red), but then if you flip it back to playback mode after it's recorded, it would possibly go dark, because it's supposed to be green (no red OR blue).