[iOS,Windows] Fix navigation bar colors not resetting when switching ShellContent

src/Controls/src/Core/Compatibility/Handlers/Shell/iOS/ShellNavBarAppearanceTracker.cs

@@ -29,6 +29,9 @@ public void ResetAppearance(UINavigationController controller)
 				navBar.BarTintColor = _defaultBarTint;
 				navBar.TintColor = _defaultTint;
 				navBar.TitleTextAttributes = _defaultTitleAttributes;
+
+				if (OperatingSystem.IsIOSVersionAtLeast(13) || OperatingSystem.IsTvOSVersionAtLeast(13))
+					UpdateiOS13NavigationBarAppearance(controller, null);
 			}
 		}
 
@@ -95,37 +98,47 @@ void UpdateiOS13NavigationBarAppearance(UINavigationController controller, Shell
 
 			var navigationBarAppearance = new UINavigationBarAppearance();
 
-			// since we cannot set the Background Image directly, let's use the alpha in the background color to determine translucence
-			if (appearance.BackgroundColor?.Alpha < 1.0f)
-			{
-				navigationBarAppearance.ConfigureWithTransparentBackground();
-				navBar.Translucent = true;
-			}
-			else
+			if (appearance is null)
 			{
 				navigationBarAppearance.ConfigureWithOpaqueBackground();
 				navBar.Translucent = false;
+				navBar.StandardAppearance = navBar.ScrollEdgeAppearance = navigationBarAppearance;
 			}
+			else
+			{
 
-			// Set ForegroundColor
-			var foreground = appearance.ForegroundColor;
+				// since we cannot set the Background Image directly, let's use the alpha in the background color to determine translucence
+				if (appearance.BackgroundColor?.Alpha < 1.0f)
+				{
+					navigationBarAppearance.ConfigureWithTransparentBackground();
+					navBar.Translucent = true;
+				}
+				else
+				{
+					navigationBarAppearance.ConfigureWithOpaqueBackground();
+					navBar.Translucent = false;
+				}
 
-			if (foreground != null)
-				navBar.TintColor = foreground.ToPlatform();
+				// Set ForegroundColor
+				var foreground = appearance.ForegroundColor;
 
-			// Set BackgroundColor
-			var background = appearance.BackgroundColor;
+				if (foreground != null)
+					navBar.TintColor = foreground.ToPlatform();
 
-			if (background != null)
-				navigationBarAppearance.BackgroundColor = background.ToPlatform();
+				// Set BackgroundColor
+				var background = appearance.BackgroundColor;
 
-			// Set TitleColor
-			var titleColor = appearance.TitleColor;
+				if (background != null)
+					navigationBarAppearance.BackgroundColor = background.ToPlatform();
 
-			if (titleColor != null)
-				navigationBarAppearance.TitleTextAttributes = new UIStringAttributes() { ForegroundColor = titleColor.ToPlatform() };
+				// Set TitleColor
+				var titleColor = appearance.TitleColor;
 
-			navBar.StandardAppearance = navBar.ScrollEdgeAppearance = navigationBarAppearance;
+				if (titleColor != null)
+					navigationBarAppearance.TitleTextAttributes = new UIStringAttributes() { ForegroundColor = titleColor.ToPlatform() };
+
+				navBar.StandardAppearance = navBar.ScrollEdgeAppearance = navigationBarAppearance;
+			}
 		}
 
 		void UpdateNavigationBarAppearance(UINavigationController controller, ShellAppearance appearance)

src/Controls/tests/TestCases.HostApp/Issues/Issue33227.cs

@@ -0,0 +1,77 @@
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 33227, "Shell NavigationBar colors persist when navigating between pages", PlatformAffected.iOS | PlatformAffected.UWP)]
+public class Issue33227 : Shell
+{
+    public Issue33227()
+    {
+        var tabBar = new TabBar { Title = "Tab1" };
+        var tab = new Tab { Title = "Tab1" };
+
+        var page1Content = new ShellContent
+        {
+            Title = "Page1",
+            ContentTemplate = new DataTemplate(() => new Issue33227Page1())
+        };
+
+        var page2Content = new ShellContent
+        {
+            Title = "Page2",
+            ContentTemplate = new DataTemplate(() => new Issue33227Page2())
+        };
+
+        tab.Items.Add(page1Content);
+        tab.Items.Add(page2Content);
+        tabBar.Items.Add(tab);
+        Items.Add(tabBar);
+    }
+}
+
+public class Issue33227Page1 : ContentPage
+{
+    public Issue33227Page1()
+    {
+        var layout = new VerticalStackLayout
+        {
+            Padding = 20,
+            Spacing = 10,
+            VerticalOptions = LayoutOptions.Center,
+            HorizontalOptions = LayoutOptions.Center
+        };
+
+        var label = new Label
+        {
+            Text = "Page1",
+            AutomationId = "Page1Label"
+        };
+
+        layout.Add(label);
+        Content = layout;
+    }
+}
+
+public class Issue33227Page2 : ContentPage
+{
+    public Issue33227Page2()
+    {
+        Shell.SetBackgroundColor(this, Colors.Yellow);
+        Shell.SetTitleColor(this, Colors.Orange);
+
+        var layout = new VerticalStackLayout
+        {
+            Padding = 20,
+            Spacing = 10,
+            VerticalOptions = LayoutOptions.Center,
+            HorizontalOptions = LayoutOptions.Center
+        };
+
+        var label = new Label
+        {
+            Text = "Page2",
+            AutomationId = "Page2Label"
+        };
+
+        layout.Add(label);
+        Content = layout;
+    }
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue33227.cs

@@ -0,0 +1,35 @@
+using Microsoft.Maui.TestCases.Tests;
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Maui.Controls.TestCases.Tests.Issues;
+
+public class Issue33227 : _IssuesUITest
+{
+    public Issue33227(TestDevice device) : base(device)
+    {
+    }
+
+    public override string Issue => "Shell NavigationBar colors persist when navigating between pages";
+
+    [Test]
+    [Category(UITestCategories.Shell)]
+    public void ShellColorsResetOnNavigation()
+    {
+#if WINDOWS
+        App.TapTab("Tab1");
+        App.WaitForElement("Page2");
+        App.Tap("Page2");
+        App.TapTab("Tab1");
+        App.WaitForElement("Page1");
+        App.Tap("Page1");
+        App.WaitForElement("Page1Label");
+#else
+        App.TapTab("Page2");
+        App.TapTab("Page1");
+        App.WaitForElement("Page1Label");
+#endif
+        VerifyScreenshot();
+    }
+}

src/Core/src/Platform/Windows/MauiToolbar.xaml.cs

@@ -86,6 +86,10 @@ internal void SetBarTextColor(WBrush? brush)
 			{
 				title.Foreground = brush;
 			}
+			else
+			{
+				title.ClearValue(CommandBar.ForegroundProperty);
+			}
 
 			_menuBarForeground = brush;
 			UpdateMenuBarForeground();