Set color after attaching palette in expand()

Tests/test_imageops.py

@@ -157,9 +157,16 @@ def test_scale():
 
 
 def test_expand_palette():
-    im = Image.open("Tests/images/hopper.gif")
-    im_expanded = ImageOps.expand(im)
-    assert_image_equal(im_expanded.convert("RGB"), im.convert("RGB"))
+    im = Image.open("Tests/images/p_16.tga")
+    im_expanded = ImageOps.expand(im, 10, (255, 0, 0))
+
+    px = im_expanded.convert("RGB").load()
+    assert px[0, 0] == (255, 0, 0)
+
+    im_cropped = im_expanded.crop(
+        (10, 10, im_expanded.width - 10, im_expanded.height - 10)
+    )
+    assert_image_equal(im_cropped, im)
 
 
 def test_colorize_2color():

src/PIL/ImageOps.py

@@ -20,7 +20,7 @@
 import functools
 import operator
 
-from . import Image
+from . import Image, ImageDraw
 
 #
 # helpers
@@ -392,10 +392,17 @@ def expand(image, border=0, fill=0):
     left, top, right, bottom = _border(border)
     width = left + image.size[0] + right
     height = top + image.size[1] + bottom
-    out = Image.new(image.mode, (width, height), _color(fill, image.mode))
+    color = _color(fill, image.mode)
     if image.mode == "P" and image.palette:
+        out = Image.new(image.mode, (width, height))
         out.putpalette(image.palette)
-    out.paste(image, (left, top))
+        out.paste(image, (left, top))
+
+        draw = ImageDraw.Draw(out)
+        draw.rectangle((0, 0, width, height), outline=color, width=border)
+    else:
+        out = Image.new(image.mode, (width, height), color)
+        out.paste(image, (left, top))
     return out
 
 

src/PIL/ImagePalette.py

@@ -115,7 +115,7 @@ class ImagePalette:
                 return self.colors[color]
             except KeyError as e:
                 # allocate new color slot
-                if isinstance(self.palette, bytes):
+                if not isinstance(self.palette, bytearray):
                     self._palette = bytearray(self.palette)
                 index = len(self.palette) // 3
                 if index >= 256:
@@ -129,9 +129,11 @@ class ImagePalette:
                         raise ValueError("cannot allocate more than 256 colors") from e
                 self.colors[color] = index
                 if index * 3 < len(self.palette):
-                    self._palette[index * 3] = color[0]
-                    self._palette[index * 3 + 1] = color[1]
-                    self._palette[index * 3 + 2] = color[2]
+                    self._palette = (
+                        self.palette[: index * 3]
+                        + bytes(color)
+                        + self.palette[index * 3 + 3 :]
+                    )
                 else:
                     self._palette += bytes(color)
                 self.dirty = 1