Try test

Tests/test_file_blp.py

@@ -20,6 +20,12 @@ def test_load_blp2_dxt1a():
         assert_image_equal_tofile(im, "Tests/images/blp/blp2_dxt1a.png")
 
 
+def test_load_blp1():
+    with Image.open("Tests/images/blp/war3mapMap.blp") as im:
+        im.convert("RGB")
+        assert_image_equal_tofile(im, "Tests/images/blp/war3mapMap.png")
+
+
 @pytest.mark.parametrize(
     "test_file",
     [

src/PIL/BlpImagePlugin.py

@@ -28,7 +28,7 @@ BLP files come in many different flavours:
   - DXT3 compression is used if alpha_encoding == 1.
   - DXT5 compression is used if alpha_encoding == 7.
 """
-
+print("foo")
 import struct
 from io import BytesIO
 
@@ -245,7 +245,7 @@ class BlpImageFile(ImageFile.ImageFile):
 
         if self.magic == b"BLP1":
             decoder = "BLP1"
-            self.mode = "RGBA"
+            self.mode = "BGRA"
         elif self.magic == b"BLP2":
             decoder = "BLP2"
             self.mode = "RGBA" if self._blp_alpha_depth else "RGB"
@@ -361,6 +361,16 @@ class BLP1Decoder(_BLPBaseDecoder):
         image.tile = [("jpeg", (0, 0) + self.size, 0, ("RGBA", ""))]
 
         b, g, r, a = image.split()
+        print(b, g, r, a)
+        if not any(
+            [a.getpixel((x, y)) for x in range(a.width) for y in range(a.height)]
+        ):
+            # try to unprotect completely transparent pictures
+            from PIL import ImageOps
+
+            a = ImageOps.invert(a)
+
+
         image = Image.merge("RGBA", (r, g, b, a))
         self.set_as_raw(image.tobytes())