diff --git a/blocked.png b/blocked.png
new file mode 100644
index 0000000..596e43f
Binary files /dev/null and b/blocked.png differ
diff --git a/two-tone.py b/two-tone.py
index c5ead60..e9f4603 100644
--- a/two-tone.py
+++ b/two-tone.py
@@ -44,15 +44,21 @@ def choose_color_pair_kmeans(counts: dict[RGB,int]) -> tuple[RGB, RGB]:
 
     def weighted_avg(colors: list[RGB]) -> RGB:
         result = [0, 0, 0]
+        total_weight = 0
         for color in colors:
             weight = counts[color]
+            total_weight += weight
             for i in range(3):
                 result[i] += weight*color[i]
-        return tuple(round(x/total_count) for x in result)
+        if total_weight == 0:
+            total_weight += 1 # Hack to handle division-by-zero
+        return tuple(round(x/total_weight) for x in result)
 
     # k-means to choose the two colors
     old_result = (None, None)
-    result = (darkest_color, lightest_color)
+    result = (min(colors, key=brightness), max(colors, key=brightness))
+    print(f"k-means using {counts=}")
+    print(f"starting value: {result}")
     while True:
         lists = ([], [])
         for color in colors:
@@ -63,7 +69,9 @@ def choose_color_pair_kmeans(counts: dict[RGB,int]) -> tuple[RGB, RGB]:
             else:
                 lists[1].append(color)
         old_result = result
+        print(f"{lists=}")
         result = tuple(weighted_avg(cs) for cs in lists)
+        print(f"updated: {result}")
         if old_result == result:
             break
     return tuple(nearest_color(x, palette) for x in result)
@@ -119,7 +127,10 @@ def two_tone(img: Image, xy1: tuple[int,int] = None, xy2: tuple[int,int] = None)
             if color not in counts:
                 counts[color] = 0
             counts[color] += 1
-    dark, light = choose_color_pair_luminance(counts)
+    #dark, light = choose_color_pair_luminance(counts)
+    print(f"choosing color pair for {xy1=}")
+    dark, light = choose_color_pair_kmeans(counts)
+    print(f"final: {dark=}, {light=}\n")
     if light == None:
         # Only one color, *ought* to be a no-op
         light = dark
@@ -138,3 +149,7 @@ blocked = img.copy()
 for x in range(0, img.width, BLOCK_SIZE):
     for y in range(0, img.height, BLOCK_SIZE):
         two_tone(blocked, (x, y), (x + BLOCK_SIZE, y + BLOCK_SIZE))
+blocked.save("blocked.png")
+for x in range(5):
+    for y in range(5):
+        blocked.putpixel((x, y), 0)