From eab2b17d640b44cf44dc6f2a2f35af465cb694ee Mon Sep 17 00:00:00 2001
From: Andrew Murray <radarhere@users.noreply.github.com>
Date: Wed, 30 Jun 2021 00:05:25 +1000
Subject: [PATCH] Do not use background or transparency index for new color

---
 Tests/test_imagepalette.py | 19 +++++++++++++++++++
 src/PIL/ImagePalette.py    | 10 +++++++++-
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/Tests/test_imagepalette.py b/Tests/test_imagepalette.py
index ee2cfdf9b2b..9c4f8acfb58 100644
--- a/Tests/test_imagepalette.py
+++ b/Tests/test_imagepalette.py
@@ -49,6 +49,25 @@ def test_getcolor():
         palette.getcolor("unknown")
 
 
+def test_getcolor_not_special():
+    im = Image.new("P", (1, 1))
+    for index, palette in {
+        # Test when the palette is not full
+        0: ImagePalette.ImagePalette(),
+        # Test when the palette is full
+        255: ImagePalette.ImagePalette("RGB", list(range(256)) * 3),
+    }.items():
+        # Do not use transparency index as a new color
+        im.info["transparency"] = index
+        index1 = palette.getcolor((0, 0, 0), im)
+        assert index1 != index
+
+        # Do not use background index as a new color
+        im.info["background"] = index1
+        index2 = palette.getcolor((0, 0, 1), im)
+        assert index2 not in (index, index1)
+
+
 def test_file(tmp_path):
 
     palette = ImagePalette.ImagePalette("RGB", list(range(256)) * 3)
diff --git a/src/PIL/ImagePalette.py b/src/PIL/ImagePalette.py
index 76c4c46d551..b0c722b29af 100644
--- a/src/PIL/ImagePalette.py
+++ b/src/PIL/ImagePalette.py
@@ -118,11 +118,19 @@ def getcolor(self, color, image=None):
                 if not isinstance(self.palette, bytearray):
                     self._palette = bytearray(self.palette)
                 index = len(self.palette) // 3
+                special_colors = ()
+                if image:
+                    special_colors = (
+                        image.info.get("background"),
+                        image.info.get("transparency"),
+                    )
+                while index in special_colors:
+                    index += 1
                 if index >= 256:
                     if image:
                         # Search for an unused index
                         for i, count in reversed(list(enumerate(image.histogram()))):
-                            if count == 0:
+                            if count == 0 and i not in special_colors:
                                 index = i
                                 break
                     if index >= 256: