[iOS] Fix Switch ThumbColor reset on iOS 26+ theme changes.

src/Controls/tests/TestCases.HostApp/Issues/Issue33783.cs

@@ -0,0 +1,61 @@
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 33783, "Switch ThumbColor not applied correctly when theme changes on iOS", PlatformAffected.iOS | PlatformAffected.macOS)]
+public class Issue33783 : ContentPage
+{
+	public Issue33783()
+	{
+		var testSwitch = new Switch
+		{
+			AutomationId = "TestSwitch",
+			OnColor = Colors.Green,
+			ThumbColor = Colors.Red,
+			IsToggled = true,
+			HorizontalOptions = LayoutOptions.Center
+		};
+
+		var lightThemeButton = new Button
+		{
+			AutomationId = "LightThemeButton",
+			Text = "Light Theme"
+		};
+
+		lightThemeButton.Clicked += (s, e) =>
+		{
+			if (Application.Current != null)
+			{
+				Application.Current.UserAppTheme = AppTheme.Light;
+			}
+		};
+
+		var darkThemeButton = new Button
+		{
+			AutomationId = "DarkThemeButton",
+			Text = "Dark Theme"
+		};
+
+		darkThemeButton.Clicked += (s, e) =>
+		{
+			if (Application.Current != null)
+			{
+				Application.Current.UserAppTheme = AppTheme.Dark;
+			}
+		};
+
+		var themeButtonsLayout = new HorizontalStackLayout
+		{
+			Spacing = 10,
+			HorizontalOptions = LayoutOptions.Center,
+			Children = { lightThemeButton, darkThemeButton }
+		};
+
+		var contentLayout = new VerticalStackLayout
+		{
+			Spacing = 20,
+			Padding = new Thickness(30),
+			Children = { testSwitch, themeButtonsLayout }
+		};
+		contentLayout.SetAppThemeColor(BackgroundColorProperty, Colors.White, Colors.Black);
+		Content = contentLayout;
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue33783.cs

@@ -0,0 +1,34 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue33783 : _IssuesUITest
+{
+	public Issue33783(TestDevice testDevice) : base(testDevice)
+	{
+	}
+
+	public override string Issue => "Switch ThumbColor not applied correctly when theme changes on iOS";
+
+	[Test, Order(0)]
+	[Category(UITestCategories.Switch)]
+	public async Task VerifySwitchThumbColorOnDarkThemeChange()
+	{
+		App.WaitForElement("DarkThemeButton");
+		App.Tap("DarkThemeButton");
+		await Task.Delay(500);
+		VerifyScreenshot("Issue33783_SwitchThumbColor_DarkTheme");
+	}
+
+	[Test, Order(1)]
+	[Category(UITestCategories.Switch)]
+	public async Task VerifySwitchThumbColorOnLightThemeChange()
+	{
+		App.WaitForElement("LightThemeButton");
+		App.Tap("LightThemeButton");
+		await Task.Delay(500);
+		VerifyScreenshot("Issue33783_SwitchThumbColor_LightTheme");
+	}
+}

src/Core/src/Handlers/Switch/SwitchHandler.iOS.cs

@@ -3,6 +3,7 @@
 using CoreFoundation;
 using Foundation;
 using Microsoft.Maui.Graphics;
+using Microsoft.Maui.Platform;
 using ObjCRuntime;
 using UIKit;
 using RectangleF = CoreGraphics.CGRect;
@@ -69,6 +70,7 @@ class SwitchProxy
 
 			NSObject? _willEnterForegroundObserver;
 			NSObject? _windowDidBecomeKeyObserver;
+			IUITraitChangeRegistration? _traitChangeRegistration;
 
 			public void Connect(ISwitch virtualView, UISwitch platformView)
 			{
@@ -83,6 +85,10 @@ public void Connect(ISwitch virtualView, UISwitch platformView)
 						if (PlatformView is not null)
 						{
 							UpdateTrackOffColor(PlatformView);
+							if (OperatingSystem.IsMacCatalystVersionAtLeast(26))
+							{
+								UpdateThumbColor(PlatformView);
+							}
 						}
 					});
 #elif IOS
@@ -95,6 +101,28 @@ public void Connect(ISwitch virtualView, UISwitch platformView)
 						}
 					});
 #endif
+
+				// iOS/MacCatalyst 26+ resets ThumbTintColor when theme changes (light/dark mode).
+				// Register for trait changes to re-apply ThumbColor after UIKit completes its styling.
+				if (OperatingSystem.IsIOSVersionAtLeast(26) || OperatingSystem.IsMacCatalystVersionAtLeast(26))
+				{
+					if (_traitChangeRegistration is not null)
+					{
+						platformView.UnregisterForTraitChanges(_traitChangeRegistration);
+					}
+
+					_traitChangeRegistration = platformView.RegisterForTraitChanges<UITraitUserInterfaceStyle>(
+						(IUITraitEnvironment view, UITraitCollection _) =>
+						{
+							if (view is UISwitch uiSwitch)
+							{
+								UpdateThumbColor(uiSwitch);
+							}
+						});
+
+					// iOS 26+ resets ThumbTintColor after initial layout, so re-apply the custom ThumbColor here.
+					UpdateThumbColor(platformView);
+				}
 			}
 
 			// Ensures the Switch track "OFF" color is updated correctly after system-level UI resets.
@@ -116,6 +144,22 @@ void UpdateTrackOffColor(UISwitch platformView)
 				});
 			}
 
+			void UpdateThumbColor(UISwitch platformView)
+			{
+				DispatchQueue.MainQueue.DispatchAsync(async () =>
+				{
+					if (VirtualView is null || PlatformView is null)
+						return;
+
+					await Task.Delay(10); // Small delay, necessary to allow UIKit to complete its internal layout and styling processes before re-applying the custom color
+
+					if (VirtualView is ISwitch view && view.ThumbColor is not null)
+					{
+						platformView.UpdateThumbColor(view);
+					}
+				});
+			}
+
 			public void Disconnect(UISwitch platformView)
 			{
 				platformView.ValueChanged -= OnControlValueChanged;
@@ -130,6 +174,11 @@ public void Disconnect(UISwitch platformView)
 					NSNotificationCenter.DefaultCenter.RemoveObserver(_windowDidBecomeKeyObserver);
 					_windowDidBecomeKeyObserver = null;
 				}
+				if (_traitChangeRegistration is not null)
+				{
+					platformView.UnregisterForTraitChanges(_traitChangeRegistration);
+					_traitChangeRegistration = null;
+				}
 			}
 
 			void OnControlValueChanged(object? sender, EventArgs e)