What specific scripts gave you partial (random) success lighting Pico keys? I tried to adapt techniques recently discussed for Alpha to Pico and Tau, but they depend on defining new mode keys and the trick of selecting one of them at the same time as you select what sounds to play. That doesn't (easily) work on Pico because there are no available mode keys... (lightbulb goes on) Perhaps it could with the nudgers disabled on keys 9 and 18.
However, Ferdinand's MIDI Illuminator does (can) work on Pico to give reference lights for various scales and layouts and to give dynamic lights for as you play them or receive MIDI notes.