Do not treat RGB as a rawmode for an RGB palette

Tests/test_imagepalette.py

@@ -179,17 +179,23 @@ def test_make_gamma_lut() -> None:
     assert lut[255] == 255
 
 
-def test_rawmode_valueerrors(tmp_path: Path) -> None:
+def test_raw() -> None:
+    data = list(range(256)) * 3
+    palette = ImagePalette.raw("RGB", data)
+    assert palette.tobytes() == bytes(data)
+
+
+def test_raw_valueerrors(tmp_path: Path) -> None:
     # Arrange
-    palette = ImagePalette.raw("RGB", list(range(256)) * 3)
+    palette = ImagePalette.raw("BGR", list(range(256)) * 3)
 
     # Act / Assert
-    with pytest.raises(ValueError):
+    with pytest.raises(ValueError, match="palette contains raw palette data"):
         palette.tobytes()
-    with pytest.raises(ValueError):
+    with pytest.raises(ValueError, match="palette contains raw palette data"):
         palette.getcolor((1, 2, 3))
     f = str(tmp_path / "temp.lut")
-    with pytest.raises(ValueError):
+    with pytest.raises(ValueError, match="palette contains raw palette data"):
         palette.save(f)
 
 

src/PIL/Image.py

@@ -2161,11 +2161,7 @@ def putpalette(
             msg = "illegal image mode"
             raise ValueError(msg)
         if isinstance(data, ImagePalette.ImagePalette):
-            if data.rawmode is not None:
-                palette = ImagePalette.raw(data.rawmode, data.palette)
-            else:
-                palette = ImagePalette.ImagePalette(palette=data.palette)
-                palette.dirty = 1
+            palette = ImagePalette.raw(data.rawmode or "RGB", data.palette)
         else:
             if not isinstance(data, bytes):
                 data = bytes(data)

src/PIL/ImagePalette.py

@@ -233,7 +233,8 @@ def save(self, fp: str | IO[str]) -> None:
 
 def raw(rawmode: str, data: Sequence[int] | bytes | bytearray) -> ImagePalette:
     palette = ImagePalette()
-    palette.rawmode = rawmode
+    if rawmode != "RGB":
+        palette.rawmode = rawmode
     palette.palette = data
     palette.dirty = 1
     return palette