From f9a3178bb34e6b28bc46d42ef88f5069ebabde32 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jo=C3=A3o=20S=2E=20O=2E=20Bueno?= <gwidion@gmail.com>
Date: Sun, 9 Oct 2022 11:47:24 -0300
Subject: [PATCH] Fix #6652: Handle translucent color used in RGB ImagePallete

---
 Tests/test_imagepalette.py | 9 +++++++++
 src/PIL/ImagePalette.py    | 8 ++++++--
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/Tests/test_imagepalette.py b/Tests/test_imagepalette.py
index 475d249ed09..0583154f732 100644
--- a/Tests/test_imagepalette.py
+++ b/Tests/test_imagepalette.py
@@ -50,6 +50,15 @@ def test_getcolor():
         palette.getcolor("unknown")
 
 
+def test_getcolor_raises_on_incompatible_color():
+    palette = ImagePalette.ImagePalette(mode="RGB")
+    # Opaque RGBA colors should work
+    palette.getcolor((0, 0, 0, 255))
+    assert palette.getcolor((0, 0, 0)) == palette.getcolor((0, 0, 0, 255))
+    with pytest.raises(ValueError):
+        palette.getcolor((0, 0, 0, 128))
+
+
 @pytest.mark.parametrize(
     "index, palette",
     [
diff --git a/src/PIL/ImagePalette.py b/src/PIL/ImagePalette.py
index b73b2cd9dd0..e407bbcd17a 100644
--- a/src/PIL/ImagePalette.py
+++ b/src/PIL/ImagePalette.py
@@ -114,9 +114,13 @@ def getcolor(self, color, image=None):
         if self.rawmode:
             raise ValueError("palette contains raw palette data")
         if isinstance(color, tuple):
-            if self.mode == "RGB":
-                if len(color) == 4 and color[3] == 255:
+            if self.mode == "RGB" and len(color) == 4:
+                if color[3] == 255:
                     color = color[:3]
+                else:
+                    raise ValueError(
+                        "RGB ImagePalette can't handle non-opaque RGBA colors"
+                    )
             elif self.mode == "RGBA":
                 if len(color) == 3:
                     color += (255,)