Steps to Reproduce

1. Create a smallest MaterialApp with transparent background and a Container with 50% alpha white(#80FFFFFF) in it.
2. Use RenderRepaintBoundary in Flutter to take a screenshot.
3. Use FlutterImageView in Android Java side to take a screenshot.
4. Use FlutterEngine.getRenderer().getBitmap(); in Java side to take a screenshot of this flutter app.

Expected results:
Step 2/3/4: A rectangular filled with #80FFFFFF centered in transparent background and the screenshot saved to a Bitmap.

Actual results:
In step 2 and 3, I get expected result.
I saved result as PNG and it looks like this in PhotoShop:

In step 4, a rectangular filled with #80808080 centered in transparent background.
I saved it to PNG:

MaterialApp(
      debugShowCheckedModeBanner: false,
      builder: (context, child) {
        return Material(
          type: MaterialType.transparency,
          child: Container(
            alignment: Alignment.center,
            color: Colors.transparent,
            child: Container(
              width: 50,
              height: 50,
              color: Color.fromARGB(128, 255, 255, 255),
            ),
          ),
        );
      },
    );