Logically invert the pin?

Sure, yes - it's here:

• https://github.com/espruino/Espruino/blo­b/master/libs/neopixel/jswrap_neopixel.c­#L28
  
• https://github.com/espruino/Espruino/blo­b/master/targets/stm32/stm32_ws2812b_dri­ver.h#L18 <--- timings
  
• https://github.com/espruino/Espruino/blo­b/master/targets/stm32/stm32_ws2812b_dri­ver.c
  
  

So it's only compiled in for WIO_LTE at the moment. I guess a more thoughtful implementation could be included for all boards though (for instance it could benchmark itself to figure out how many iterations it has to idle for - in fact STM32's jshDelayMicroseconds already does that).