While not a source I would wager that the LEDs are already driven close to the bandgap (for efficiency's sake) and meaningfully lower voltages would cease to pr

While not a source I would wager that the LEDs are already driven close to the bandgap (for efficiency's sake) and meaningfully lower voltages would cease to produce any light output - necessitating PWM to control brightness. I could plausibly see some color shift at close to bandgap voltage if there isn't a perfect uniformity in bandgap across a diode, inconsistent or even just gaussian distributed doping would result in some holes being preferentially excited if there isn't a sufficient surplus V?