--- rxvt-unicode/src/command.C	2016/06/21 12:03:56	1.570
+++ rxvt-unicode/src/command.C	2016/06/30 16:56:41	1.575
@@ -3336,6 +3336,20 @@
     }
 }
 
+static unsigned int
+colorcube_index (unsigned int idx_r,
+                 unsigned int idx_g,
+                 unsigned int idx_b)
+{
+  assert (idx_r < Red_levels);
+  assert (idx_g < Green_levels);
+  assert (idx_b < Blue_levels);
+
+  return idx_r * Blue_levels * Green_levels +
+         idx_g * Blue_levels +
+         idx_b;
+}
+
 /*
  * Find the nearest color slot in the hidden color cube,
  * adapt its value to the 24bit RGB color.
@@ -3343,19 +3357,71 @@
 unsigned int
 rxvt_term::map_rgb24_color (unsigned int r, unsigned int g, unsigned int b)
 {
-  unsigned int idx_r = (r & 0xff) / (0xff / (Red_levels - 1));
-  unsigned int idx_g = (g & 0xff) / (0xff / (Green_levels - 1));
-  unsigned int idx_b = (b & 0xff) / (0xff / (Blue_levels - 1));
-  unsigned int idx;
-
-  idx = minTermCOLOR24 + idx_r * Blue_levels * Green_levels +
-                         idx_g * Blue_levels +
-                         idx_b;
+  r &= 0xff;
+  g &= 0xff;
+  b &= 0xff;
+
+  unsigned int color = (r << 16) | (g << 8) | b;
+  unsigned int idx_r = r / (0xff / (Red_levels - 1));
+  unsigned int idx_g = g / (0xff / (Green_levels - 1));
+  unsigned int idx_b = b / (0xff / (Blue_levels - 1));
+  unsigned int idx = colorcube_index (idx_r, idx_g, idx_b);
+
+  if (rgb24_color[idx] == color)
+    return idx + minTermCOLOR24;
+
+  /* we allow one of the 6 directly neighbouring colours */
+  /* to replace the current color, if they not used recently */
+  static const signed char dxyz[][3] = {
+     0,  0,  0,
+     0,  0, +1,
+     0,  0, -1,
+     0, +1,  0,
+     0, -1,  0,
+    +1,  0,  0,
+    -1,  0,  0,
+  };
+
+  for (int n = 0; n < ecb_array_length (dxyz); ++n)
+    {
+      int r = idx_r + dxyz[n][0];
+      int g = idx_r + dxyz[n][1];
+      int b = idx_r + dxyz[n][2];
+
+      if (!IN_RANGE_EXC (r, 0, Red_levels))
+        continue;
+
+      if (!IN_RANGE_EXC (g, 0, Green_levels))
+        continue;
+
+      if (!IN_RANGE_EXC (b, 0, Blue_levels))
+        continue;
+
+      unsigned int index = colorcube_index (r, g, b);
+
+      // minor issue: could update index 0 few more times
+      if ((rgb24_seqno[index] | rgb24_color[index]) == 0)
+        {
+          idx = index;
+          goto update;
+        }
+
+      if (rgb24_color[index] == color)
+        return index + minTermCOLOR24;
+
+      // like (rgb24_seqno[idx] > rgb24_seqno[index])
+      // but also handles wrap around values good enough
+      if ((uint16_t)(rgb24_seqno[idx] - rgb24_seqno[index]) < 0x7fff)
+        idx = index;
+    }
+
+update:
+  rgb24_color[idx] = color;
+  rgb24_seqno[idx] = ++rgb24_sequence;
 
+  idx += minTermCOLOR24;
   pix_colors_focused [idx].free (this);
-  pix_colors_focused [idx].set (this, rgba (r * 0x0101,
-                                            g * 0x0101,
-                                            b * 0x0101));
+  pix_colors_focused [idx].set (this, rgba (r * 0x0101, g * 0x0101, b * 0x0101));
   update_fade_color (idx, false);
 
   return idx;