Naively, I didn't take into account that these LEDs were RGBW, so I tried running the example code:

import machine, neopixel
np = neopixel.NeoPixel(machine.Pin(4), 8)
np.fill((0, 64, 0))
np.write()

Of course, that results in odd behavior. Not all LEDs light up, or light up in odd colors.

Simply changing the 3 to 4 for self.buf and adding a w entry to the tuple in neopixel.py makes it work correctly. Of course, doing that directly would break it for folks with regular RGB LEDs. What would be the appropriate design choice here?

I'd be willing to submit a PR if you folks tell me how you want it to act.