anchor.diff:      int count = 0;
       for (int i = _lowerIndex; i <= _upperIndex; i++) {
         final Color color = colors[i];
  -      count += histogram[color];
  +      count += histogram[color].value;
         if (color.red > maxRed) {
           maxRed = color.red;
         }
  
positive.code: 
    List<PaletteColor> _quantizePixels(
      int maxColors,
      Map<Color, int> histogram,
    ) {
      int volumeComparator(_ColorVolumeBox a, _ColorVolumeBox b) {
        return b.getVolume().compareTo(a.getVolume());
  
negative.code:       final Color quantizedColor = quantizeColor(pixel);
        final Color colorKey = quantizedColor.withAlpha(0xff);
        // Skip pixels that are entirely transparent.
        if (quantizedColor.alpha == 0x0) {
          continue;
        }
        if (currentColor != colorKey) {
          currentColor = colorKey;
          currentColorCount = hist[colorKey];
          if (currentColorCount == null) {
            hist[colorKey] = currentColorCount = _ColorCount();
          }
        }
        currentColorCount.value = currentColorCount.value + 1;
      }
      // Now let's remove any colors that the filters want to ignore.
      hist.removeWhere((Color color) {
        return _shouldIgnoreColor(color);
      });
      if (hist.length <= maxColors) {
  