Well, it just became even more interesting. We have a piece from circuitscribe that shines red or blue depending on the current direction. We made it glow red AND blue.
I would not believe this myself if I did not see. Look at the scheme of the circuit. I could not take a picture, the effect was not stable.
My guess is, static charge shifts an electron-hole balance and leads to weak recombination.
Pity the effect is so weak and unstable. We can observe it at night, and when we are not ready with instruments.