// color = 0 to 255
static int pixelsWith332Color(RGBImage img, int color) {
  int count = 0;
  for (int rgb : img.pixels)
    if (to332(rgb) == (byte) color)
      ++count;
  ret count;
}

// color = e.g. "053"
static int pixelsWith332Color(RGBImage img, S color) {
  ret pixelsWith332Color(img, color332toByte(color));
}