This is an augmentation for a tattoo -- essentially a self-encapsulated implantable LED surrounded either by a glucose battery or an inductive power coupler. The latter is probably less healthy and more bakeable.
Possible applications: tattoo figures whose eyes glow in the dark, animated tattoos,
a subcutaneous illuminated glucose readout screen for diabetics, a pulse/oxygen/temperature implant for medical monitoring/biofeedback, or "ET style" fingertips, built-in emergency forehead lamp for miners, tattoo of a changing neon sign, etc.
Implementing a color-changing LED might be neat and trivial since such LEDs are already on the market.
I imagine the batteries will have to shrink a little bit first, but I think you can get a visible glow from an LED with very little current.