from neopixel import NeoPixel
from machine import Pin
from time import sleep

pixels = NeoPixel(Pin(4), 16)

while True:
  # Red
  pixels.fill((255, 0, 0))
  pixels.write()
  sleep(0.5)
  # Green
  pixels.fill((0, 255, 0))
  pixels.write()
  sleep(0.5)