static Pair<RGBImage, Float> rgbMostSimilarImage(RGBImage pat, Iterable<RGBImage> images, float similarity) {
  new Best<RGBImage> best;
  for (RGBImage img : unnull(images)) {
    float sim = rgbImageSimilarity(pat, img, similarity);
    if (best.put(img, sim))
      similarity = sim;
  }
  ret pair(best!, (float) best.score());
}