feat: Support for DefaultTextForegroundThemeBrush

src/Uno.UI.RuntimeTests/Helpers/StyleHelper.cs

@@ -1,7 +1,7 @@
 using System;
 using System.Collections.Generic;
-using System.Text;
 using System.Linq;
+using System.Text;
 using Uno.Disposables;
 using Windows.UI.Xaml;
 using Windows.UI.Xaml.Controls;
@@ -81,7 +81,14 @@ public static IDisposable UseFluentStyles()
 			var xcr = new Microsoft.UI.Xaml.Controls.XamlControlsResources();
 			resources.MergedDictionaries.Insert(0, xcr);
 
-			return new DisposableAction(() => resources.MergedDictionaries.Remove(xcr));
+			// Force default brushes to be reloaded
+			UIElement.ResetDefaultThemeBrushes();
+
+			return new DisposableAction(() =>
+			{
+				resources.MergedDictionaries.Remove(xcr);
+				UIElement.ResetDefaultThemeBrushes();
+			});
 #endif
 		}
 	}

src/Uno.UI/UI/Xaml/Application.cs

@@ -415,6 +415,7 @@ private void SetRequestedTheme(ApplicationTheme requestedTheme)
 
 		private void OnResourcesChanged(ResourceUpdateReason updateReason)
 		{
+			UIElement.ResetDefaultThemeBrushes();
 			foreach (var contentRoot in WinUICoreServices.Instance.ContentRootCoordinator.ContentRoots)
 			{
 				if (GetTreeRoot(contentRoot) is { } root)

src/Uno.UI/UI/Xaml/Controls/ContentPresenter/ContentPresenter.cs

@@ -52,6 +52,7 @@ public partial class ContentPresenter : FrameworkElement, ICustomClippingElement
 
 		private void InitializeContentPresenter()
 		{
+			SetDefaultForeground(ForegroundProperty);
 		}
 
 		/// <summary>

src/Uno.UI/UI/Xaml/Controls/TextBlock/TextBlock.cs

@@ -43,6 +43,8 @@ public partial class TextBlock : DependencyObject
 		public TextBlock()
 		{
 			IFrameworkElementHelper.Initialize(this);
+			SetDefaultForeground(ForegroundProperty);
+
 			InitializeProperties();
 
 			InitializePartial();

src/Uno.UI/UI/Xaml/Controls/TextBlock/TextBlock.skia.cs

@@ -25,6 +25,7 @@ partial class TextBlock : FrameworkElement, IBlock
 
 		public TextBlock()
 		{
+			SetDefaultForeground(ForegroundProperty);
 			_textVisual = new TextVisual(Visual.Compositor, this);
 
 			Visual.Children.InsertAtBottom(_textVisual);

src/Uno.UI/UI/Xaml/FrameworkElement.cs

@@ -964,10 +964,7 @@ internal virtual void UpdateThemeBindings(ResourceUpdateReason updateReason)
 		/// <param name="foregroundProperty">The appropriate property for the calling instance.</param>
 		private protected void SetDefaultForeground(DependencyProperty foregroundProperty)
 		{
-			(this).SetValue(foregroundProperty,
-							Application.Current == null || Application.Current.RequestedTheme == ApplicationTheme.Light
-								? SolidColorBrushHelper.Black
-								: SolidColorBrushHelper.White, DependencyPropertyValuePrecedences.DefaultValue);
+			(this).SetValue(foregroundProperty, UIElement.GetDefaultTextBrush(), DependencyPropertyValuePrecedences.DefaultValue);
 		}
 
 		#region AutomationPeer

src/Uno.UI/UI/Xaml/UIElement.cs

@@ -30,6 +30,9 @@
 using Windows.UI.Composition;
 using Windows.Graphics.Display;
 using Uno.UI.Extensions;
+using Windows.UI.Xaml.Documents;
+using Windows.ApplicationModel.Core;
+using Uno.UI.Xaml.Media;
 
 #if __IOS__
 using UIKit;
@@ -44,6 +47,8 @@ public partial class UIElement : DependencyObject, IXUidProvider, IUIElement
 
 		private static readonly Type[] _bringIntoViewRequestedArgs = new[] { typeof(BringIntoViewRequestedEventArgs) };
 
+		private static Brush _defaultTextBrush;
+
 		private readonly SerialDisposable _clipSubscription = new SerialDisposable();
 		private string _uid;
 
@@ -183,6 +188,31 @@ internal virtual bool GetDefaultValue2(DependencyProperty property, out object d
 			return false;
 		}
 
+		internal static void ResetDefaultThemeBrushes()
+		{
+			_defaultTextBrush = null;
+		}
+
+		internal static Brush GetDefaultTextBrush()
+		{
+			if (_defaultTextBrush is null)
+			{
+				if (Application.Current.Resources.TryGetValue("DefaultTextForegroundThemeBrush", out var defaultBrushObject) &&
+					defaultBrushObject is Brush defaultBrush)
+				{
+					_defaultTextBrush = defaultBrush;
+				}
+				else
+				{
+					// Fallback to black/white
+					_defaultTextBrush = CoreApplication.RequestedTheme == Uno.Helpers.Theming.SystemTheme.Dark ?
+						SolidColorBrushHelper.White : SolidColorBrushHelper.Black;
+				}
+			}
+
+			return _defaultTextBrush;
+		}
+
 		public Vector2 ActualSize => new Vector2((float)GetActualWidth(), (float)GetActualHeight());
 
 		/// <summary>