I love simple light-based data transmission stuff. I've seen it included in things like guitar pedals that have just a few config bits that someone might want to change infrequently. An app to change some settings can be as simple as just a little webpage! So simple!
Here's a (tiny) demo of this for my PCB business card project from years ago [1]. If IIRC this proof of concept was as simple as using a phototransitor on a GPIO connected to the UART peripheral with a very low baud rate.
Could set the earrings on a phone screen and transfer the patterns over. Sounds like a fun project.
1: https://en.m.wikipedia.org/wiki/Timex_Datalink