Why do I see bright purple light with eyes closed?

Afterimage. Groups of receptors in the retina modify the signal they send to the brain when looking at the same image for a while. They may even send an opposite signal as they balance the inputs for maximum vision. Looking at a yellow light will often cause a purple afterimage for a few minutes. It is harmless. Enjoy the show.
Afterimage. This color is generated by the retina as it changes the level of current sent to the brain with the change of light signal.