Repository: flutter
Issue: Overlay content scroll should not change Appbar's Background Color
Labels: framework,f: material design,has reproducible steps,P2,team-design,triaged-design,found in release: 3.27,found in release: 3.28

As per [material 3 guide for Appbar](https://m3.material.io/components/top-app-bar/overview). The Appbar should  apply a container fill color to separate app bar from body content. This works well when using the Flutter app bar.

But when the body Contains an overlay with a scrollable the Appbar color changes when scrolling the overlay content. A  simple reproducible for this is using an autoComplete widget.

I may be wrong but My understanding is overlay is not a part of the body content.

### Steps to reproduce

1. Run the below code sample
2. tap the input and scroll the overlay


### Expected results

App bar should not change color

### Actual results

App bar is changing the color

### Code sample

<details open><summary>Code sample</summary>

```dart
import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: const Text('Autocomplete Basic'),
        ),
        body: const Center(
          child: Padding(
            padding: EdgeInsets.all(10.0),
            child: AutocompleteText(),
          ),
        ),
      ),
    );
  }
}

class AutocompleteText extends StatelessWidget {
  const AutocompleteText({Key? key}) : super(key: key);
  static const List<String> data = <String>[
    'Adrian',
    'Axel',
    'jhonn',
    'bobcat',
    'chameleon',
    'Oliver',
    'William',
    'Ethan',
    'Everett',
    'Jayden',
  ];

  @override
  Widget build(BuildContext context) {
    return Autocomplete<String>(
      optionsViewOpenDirection: OptionsViewOpenDirection.up,
      optionsBuilder: (TextEditingValue textEditingValue) {
        if (textEditingValue.text == '') {
          return const Iterable<String>.empty();
        }
        return data.where((String option) {
          return option.contains(textEditingValue.text.toLowerCase());
        });
      },
      onSelected: (String selection) {
        debugPrint('You just selected $selection');
      },
    );
  }
}

```

</details>


### Screenshots or Video

<details open>
<summary>Screenshots / Video demonstration</summary>

[Upload media here]

</details>


### Logs

<details open><summary>Logs</summary>

```console

```

</details>


### Flutter Doctor output

<details open><summary>Doctor output</summary>

```console
Flutter (Channel master, 3.28.0-1.0.pre.64, on macOS 15.1.1 24B2091 darwin-arm64, locale en-IN)
    • Flutter version 3.28.0-1.0.pre.64 on channel master at /Users/mahesh/Development/flutter_master
```

```
[✓] Flutter (Channel stable, 3.27.0, on macOS 15.1.1 24B2091 darwin-arm64, locale en-IN)
    • Flutter version 3.27.0 on channel stable at /Users/mahesh/Development/flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 8495dee1fd (2 days ago), 2024-12-10 14:23:39 -0800
    • Engine revision 83bacfc525
    • Dart version 3.6.0
    • DevTools version 2.40.2

[✓] Android toolchain - develop for Android devices (Android SDK version 34.0.0)
    • Android SDK at /Users/mahesh/Library/Android/sdk
    • Platform android-35, build-tools 34.0.0
    • ANDROID_HOME = /Users/mahesh/Library/Android/sdk
    • Java binary at: /Applications/Android Studio.app/Contents/jbr/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 17.0.11+0-17.0.11b1207.24-11852314)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 16.0)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Build 16A242d
    • CocoaPods version 1.16.2

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 2024.1)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 17.0.11+0-17.0.11b1207.24-11852314)

[✓] IntelliJ IDEA Community Edition (version 2021.2.1)
    • IntelliJ at /Applications/IntelliJ IDEA CE.app
    • Flutter plugin version 61.2.4
    • Dart plugin version 212.5080.8

[✓] VS Code (version 1.94.0)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.100.0

[✓] Connected device (3 available)
    • macOS (desktop)                 • macos                 • darwin-arm64   • macOS 15.1.1 24B2091 darwin-arm64
    • Mac Designed for iPad (desktop) • mac-designed-for-ipad • darwin         • macOS 15.1.1 24B2091 darwin-arm64
    • Chrome (web)                    • chrome                • web-javascript • Google Chrome 128.0.6613.85

[✓] Network resources
    • All expected network resources are available.

• No issues found!
```

</details>