Fix dayPeriodColor handling of non-MaterialStateColors (#139845)

## Description

This fixes the handling of `dayPeriodColor` on the `TimePicker` so that if it's a non-`MaterialStateColor`, it only applies the color to the selected state, but otherwise uses the given `MaterialStateColor` to get custom behavior.

## Related Issues
 - Fixes https://github.com/flutter/flutter/issues/139445

## Tests
 - Added tests for both non-`MaterialStateColor` and `MaterialStateColor` cases.

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

@@ -8,6 +8,7 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart';
 
 import 'button_style.dart';
+import 'colors.dart';
 import 'input_decorator.dart';
 import 'material_state.dart';
 import 'theme.dart';
@@ -43,7 +44,7 @@ class TimePickerThemeData with Diagnosticable {
     this.cancelButtonStyle,
     this.confirmButtonStyle,
     this.dayPeriodBorderSide,
-    this.dayPeriodColor,
+    Color? dayPeriodColor,
     this.dayPeriodShape,
     this.dayPeriodTextColor,
     this.dayPeriodTextStyle,
@@ -61,7 +62,7 @@ class TimePickerThemeData with Diagnosticable {
     this.inputDecorationTheme,
     this.padding,
     this.shape,
-  });
+  }) : _dayPeriodColor = dayPeriodColor;
 
   /// The background color of a time picker.
   ///
@@ -102,7 +103,21 @@ class TimePickerThemeData with Diagnosticable {
   /// brightness is [Brightness.dark].
   /// If the segment is not selected, [Colors.transparent] is used to allow the
   /// [Dialog]'s color to be used.
-  final Color? dayPeriodColor;
+  Color? get dayPeriodColor {
+    if (_dayPeriodColor == null || _dayPeriodColor is MaterialStateColor) {
+      return _dayPeriodColor;
+    }
+    return MaterialStateColor.resolveWith((Set<MaterialState> states) {
+      if (states.contains(MaterialState.selected)) {
+        return _dayPeriodColor;
+      }
+      // The unselected day period should match the overall picker dialog color.
+      // Making it transparent enables that without being redundant and allows
+      // the optional elevation overlay for dark mode to be visible.
+      return Colors.transparent;
+    });
+  }
+  final Color? _dayPeriodColor;
 
   /// The shape of the day period that the time picker uses.
   ///

packages/flutter/test/material/time_picker_theme_test.dart

@@ -18,7 +18,7 @@ void main() {
     expect(identical(TimePickerThemeData.lerp(data, data, 0.5), data), true);
   });
 
-  test('TimePickerThemeData null fields by default', () {
+  test('TimePickerThemeData has null fields by default', () {
     const TimePickerThemeData timePickerTheme = TimePickerThemeData();
     expect(timePickerTheme.backgroundColor, null);
     expect(timePickerTheme.cancelButtonStyle, null);
@@ -64,7 +64,7 @@ void main() {
       cancelButtonStyle: ButtonStyle(foregroundColor: MaterialStatePropertyAll<Color>(Color(0xfffffff1))),
       confirmButtonStyle: ButtonStyle(foregroundColor: MaterialStatePropertyAll<Color>(Color(0xfffffff2))),
       dayPeriodBorderSide: BorderSide(color: Color(0xfffffff3)),
-      dayPeriodColor: Color(0xfffffff4),
+      dayPeriodColor: Color(0x00000000),
       dayPeriodShape: RoundedRectangleBorder(
         side: BorderSide(color: Color(0xfffffff5)),
       ),
@@ -102,7 +102,7 @@ void main() {
       'cancelButtonStyle: ButtonStyle#00000(foregroundColor: MaterialStatePropertyAll(Color(0xfffffff1)))',
       'confirmButtonStyle: ButtonStyle#00000(foregroundColor: MaterialStatePropertyAll(Color(0xfffffff2)))',
       'dayPeriodBorderSide: BorderSide(color: Color(0xfffffff3))',
-      'dayPeriodColor: Color(0xfffffff4)',
+      'dayPeriodColor: Color(0x00000000)',
       'dayPeriodShape: RoundedRectangleBorder(BorderSide(color: Color(0xfffffff5)), BorderRadius.zero)',
       'dayPeriodTextColor: Color(0xfffffff6)',
       'dayPeriodTextStyle: TextStyle(inherit: true, color: Color(0xfffffff7))',
@@ -764,6 +764,41 @@ void main() {
     final InputDecoration hourDecoration = _textField(tester, '7').decoration!;
     expect(hourDecoration.fillColor?.value, timePickerTheme.hourMinuteColor?.value);
   });
+
+  testWidgetsWithLeakTracking('Time picker dayPeriodColor does the right thing with non-MaterialStateColor', (WidgetTester tester) async {
+    final TimePickerThemeData timePickerTheme = _timePickerTheme().copyWith(dayPeriodColor: Colors.red);
+    final ThemeData theme = ThemeData(timePickerTheme: timePickerTheme);
+    await tester.pumpWidget(_TimePickerLauncher(themeData: theme, entryMode: TimePickerEntryMode.input));
+    await tester.tap(find.text('X'));
+    await tester.pumpAndSettle(const Duration(seconds: 1));
+
+    final Material amMaterial = _textMaterial(tester, 'AM');
+    expect(amMaterial.color, Colors.red);
+
+    final Material pmMaterial = _textMaterial(tester, 'PM');
+    expect(pmMaterial.color, Colors.transparent);
+  });
+
+  testWidgetsWithLeakTracking('Time picker dayPeriodColor does the right thing with MaterialStateColor', (WidgetTester tester) async {
+    final MaterialStateColor testColor = MaterialStateColor.resolveWith((Set<MaterialState> states) {
+      if (states.contains(MaterialState.selected)) {
+        return Colors.green;
+      }
+      return Colors.blue;
+    });
+
+    final TimePickerThemeData timePickerTheme = _timePickerTheme().copyWith(dayPeriodColor: testColor);
+    final ThemeData theme = ThemeData(timePickerTheme: timePickerTheme);
+    await tester.pumpWidget(_TimePickerLauncher(themeData: theme, entryMode: TimePickerEntryMode.input));
+    await tester.tap(find.text('X'));
+    await tester.pumpAndSettle(const Duration(seconds: 1));
+
+    final Material amMaterial = _textMaterial(tester, 'AM');
+    expect(amMaterial.color, Colors.green);
+
+    final Material pmMaterial = _textMaterial(tester, 'PM');
+    expect(pmMaterial.color, Colors.blue);
+  });
 }
 
 final Color _selectedColor = Colors.green[100]!;