Paint backgroundColor in CircularProgressIndicator (#28004)

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

diff --git a/packages/flutter/lib/src/material/progress_indicator.dart b/packages/flutter/lib/src/material/progress_indicator.dart
index 98d1c71..2b58b59 100644
--- a/packages/flutter/lib/src/material/progress_indicator.dart
+++ b/packages/flutter/lib/src/material/progress_indicator.dart
@@ -316,6 +316,7 @@
 
 class _CircularProgressIndicatorPainter extends CustomPainter {
   _CircularProgressIndicatorPainter({
+    this.backgroundColor,
     this.valueColor,
     this.value,
     this.headValue,
@@ -330,6 +331,7 @@
          ? value.clamp(0.0, 1.0) * _sweep
          : math.max(headValue * 3 / 2 * math.pi - tailValue * 3 / 2 * math.pi, _epsilon);
 
+  final Color backgroundColor;
   final Color valueColor;
   final double value;
   final double headValue;
@@ -352,6 +354,13 @@
       ..color = valueColor
       ..strokeWidth = strokeWidth
       ..style = PaintingStyle.stroke;
+    if (backgroundColor != null) {
+      final Paint backgroundPaint = Paint()
+        ..color = backgroundColor
+        ..strokeWidth = strokeWidth
+        ..style = PaintingStyle.stroke;
+      canvas.drawArc(Offset.zero & size, 0, _sweep, false, backgroundPaint);
+    }
 
     if (value == null) // Indeterminate
       paint.strokeCap = StrokeCap.square;
@@ -361,7 +370,8 @@
 
   @override
   bool shouldRepaint(_CircularProgressIndicatorPainter oldPainter) {
-    return oldPainter.valueColor != valueColor
+    return oldPainter.backgroundColor != backgroundColor
+        || oldPainter.valueColor != valueColor
         || oldPainter.value != value
         || oldPainter.headValue != headValue
         || oldPainter.tailValue != tailValue
@@ -478,6 +488,7 @@
         ),
         child: CustomPaint(
           painter: _CircularProgressIndicatorPainter(
+            backgroundColor: widget.backgroundColor,
             valueColor: widget._getValueColor(context),
             value: widget.value, // may be null
             headValue: headValue, // remaining arguments are ignored if widget.value is not null

packages/flutter/test/material/progress_indicator_test.dart

diff --git a/packages/flutter/test/material/progress_indicator_test.dart b/packages/flutter/test/material/progress_indicator_test.dart
index 6430d1c..bae43cf 100644
--- a/packages/flutter/test/material/progress_indicator_test.dart
+++ b/packages/flutter/test/material/progress_indicator_test.dart
@@ -228,6 +228,26 @@
     expect(find.byType(CircularProgressIndicator), paints..arc(strokeWidth: 16.0));
   });
 
+  testWidgets('CircularProgressIndicator paint background color', (WidgetTester tester) async {
+    const Color green = Color(0xFF00FF00);
+    const Color blue = Color(0xFF0000FF);
+
+    await tester.pumpWidget(const CircularProgressIndicator(
+      valueColor: AlwaysStoppedAnimation<Color>(blue),
+    ));
+
+    expect(find.byType(CircularProgressIndicator), paintsExactlyCountTimes(#drawArc, 1));
+    expect(find.byType(CircularProgressIndicator), paints..arc(color: blue));
+
+    await tester.pumpWidget(const CircularProgressIndicator(
+      backgroundColor: green,
+      valueColor: AlwaysStoppedAnimation<Color>(blue),
+    ));
+
+    expect(find.byType(CircularProgressIndicator), paintsExactlyCountTimes(#drawArc, 2));
+    expect(find.byType(CircularProgressIndicator), paints..arc(color: green)..arc(color: blue));
+  });
+
   testWidgets('Indeterminate RefreshProgressIndicator keeps spinning until end of time (approximate)', (WidgetTester tester) async {
     // Regression test for https://github.com/flutter/flutter/issues/13782