[ExpansionPanel] Exposes color property of MaterialSlice (#71657)

packages/flutter/lib/src/material/expansion_panel.dart

@@ -78,6 +78,7 @@ class ExpansionPanel {
     required this.body,
     this.isExpanded = false,
     this.canTapOnHeader = false,
+    this.backgroundColor,
   }) : assert(headerBuilder != null),
        assert(body != null),
        assert(isExpanded != null),
@@ -101,6 +102,10 @@ class ExpansionPanel {
   /// Defaults to false.
   final bool canTapOnHeader;
 
+  /// Defines the background color of the panel.
+  ///
+  /// Defaults to [ThemeData.cardColor].
+  final Color? backgroundColor;
 }
 
 /// An expansion panel that allows for radio-like functionality.
@@ -123,11 +128,13 @@ class ExpansionPanelRadio extends ExpansionPanel {
     required ExpansionPanelHeaderBuilder headerBuilder,
     required Widget body,
     bool canTapOnHeader = false,
+    Color? backgroundColor,
   }) : assert(value != null),
       super(
         body: body,
         headerBuilder: headerBuilder,
         canTapOnHeader: canTapOnHeader,
+        backgroundColor: backgroundColor,
       );
 
   /// The value that uniquely identifies a radio panel so that the currently
@@ -530,6 +537,7 @@ class _ExpansionPanelListState extends State<ExpansionPanelList> {
       items.add(
         MaterialSlice(
           key: _SaltedKey<BuildContext, int>(context, index * 2),
+          color: child.backgroundColor,
           child: Column(
             children: <Widget>[
               header,

packages/flutter/test/material/expansion_panel_test.dart

@@ -1458,4 +1458,75 @@ void main() {
       ' possible elevation values.'
     ));
   });
+
+  testWidgets('ExpansionPanel.panelColor test', (WidgetTester tester) async {
+    const Color firstPanelColor = Colors.red;
+    const Color secondPanelColor = Colors.brown;
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: SingleChildScrollView(
+          child: ExpansionPanelList(
+            expansionCallback: (int _index, bool _isExpanded) {},
+            children: <ExpansionPanel>[
+              ExpansionPanel(
+                backgroundColor: firstPanelColor,
+                headerBuilder: (BuildContext context, bool isExpanded) {
+                  return const Text('A');
+                },
+                body: const SizedBox(height: 100.0),
+              ),
+              ExpansionPanel(
+                backgroundColor: secondPanelColor,
+                headerBuilder: (BuildContext context, bool isExpanded) {
+                  return const Text('B');
+                },
+                body: const SizedBox(height: 100.0),
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+
+    final MergeableMaterial mergeableMaterial = tester.widget(find.byType(MergeableMaterial));
+
+    expect((mergeableMaterial.children.first as MaterialSlice).color, firstPanelColor);
+    expect((mergeableMaterial.children.last as MaterialSlice).color, secondPanelColor);
+  });
+
+  testWidgets('ExpansionPanelRadio.backgroundColor test', (WidgetTester tester) async {
+    const Color firstPanelColor = Colors.red;
+    const Color secondPanelColor = Colors.brown;
+
+    await tester.pumpWidget(MaterialApp(
+      home: SingleChildScrollView(
+        child: ExpansionPanelList.radio(
+          children: <ExpansionPanelRadio>[
+            ExpansionPanelRadio(
+              backgroundColor: firstPanelColor,
+              headerBuilder: (BuildContext context, bool isExpanded) {
+                return const Text('A');
+              },
+              body: const SizedBox(height: 100.0),
+              value: 0,
+            ),
+            ExpansionPanelRadio(
+              backgroundColor: secondPanelColor,
+              headerBuilder: (BuildContext context, bool isExpanded) {
+                return const Text('B');
+              },
+              body: const SizedBox(height: 100.0),
+              value: 1,
+            ),
+          ],
+        ),
+      ),
+    ));
+
+    final MergeableMaterial mergeableMaterial = tester.widget(find.byType(MergeableMaterial));
+
+    expect((mergeableMaterial.children.first as MaterialSlice).color, firstPanelColor);
+    expect((mergeableMaterial.children.last as MaterialSlice).color, secondPanelColor);
+  });
 }