Nick, thanks for porting that!
While we are discussing this (I too have been chasing this with the somewhat disappointing implementation of HSLuv), I was wondering -
Does anybody know - Is there a <$100 solution to color calibrate for a given RGB LED? For example, are there individual LEDs with reliable reference specs that we can use as a spectrometer to plot a curve for whatever cheap WS281X we just bought 1000 of?