Not sure if this is helpful at all, but I have two effects pedals on which the lights are ridiculously bright - ludicrously so, to the point that they’re even distracting in a well lit room. I stuck some opaque tape over the lights, so that I could still see them when they flashed, but not so bright as to feel you’d been staring at the sun for fourteen hours. Stupid solution in some ways, but kind of works.. not sure how practical it is for a synth with lots of leds though