Multi-color is probably not really possible at a reasonable price point because you'd need twice as many vias and traces in the same space for RGB compared to just R. You _can_ get it manufactured, just not in low quantities at a price anyone would be willing to pay. There are 1.1x1.1mm addressable LEDs available[0] which should be quite doable, but those require quite a high voltage and have an unacceptably high idle power consumption: a 52-LED matrix would draw 15mA with all the LEDs off!

As to single-color non-red: the main advantage of red LEDs is that they can operate on a very low voltage. The exact same board with blue LEDs would have a significantly shorter battery life - if it's even possible at all. These earrings are probably using two SR521 batteries, which start at about 1.55V and discharge to about 1V[1] - so the earring is operating on 3.1V to 2V. You can get red LEDs which work with as little as 1.7V, but blue LEDs need about 3V to operate _at all_. You'd either have about 1/3rd of the battery life, or you'd have to add a third battery.

[0]: https://www.adafruit.com/product/5849

[1]: https://img5083.weyesimg.com/uploads/xtk5s4z6.allweyes.com/i...