Parse brushes during compile time.

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/AvaloniaXamlIlLanguageParseIntrinsics.cs

@@ -207,6 +207,20 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                 return true;
             }
 
+            if (types.IBrush.IsAssignableFrom(type))
+            {
+                if (Color.TryParse(text, out Color color))
+                {
+                    var brushTypeRef = new XamlAstClrTypeReference(node, types.ImmutableSolidColorBrush, false);
+
+                    result = new XamlAstNewClrObjectNode(node, brushTypeRef,
+                        types.ImmutableSolidColorBrushConstructorColor,
+                        new List<IXamlAstValueNode> { new XamlConstantNode(node, types.UInt, color.ToUint32()) });
+
+                    return true;
+                }
+            }
+
             result = null;
             return false;
         }

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlWellKnownTypes.cs

@@ -80,7 +80,10 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
         public IXamlType ColumnDefinitions { get; }
         public IXamlType Classes { get; }
         public IXamlMethod ClassesBindMethod { get; }
-        public IXamlProperty StyledElementClassesProperty { get; set; }
+        public IXamlProperty StyledElementClassesProperty { get; }
+        public IXamlType IBrush { get; }
+        public IXamlType ImmutableSolidColorBrush { get; }
+        public IXamlConstructor ImmutableSolidColorBrushConstructorColor { get; }
 
         public AvaloniaXamlIlWellKnownTypes(TransformerConfiguration cfg)
         {
@@ -178,6 +181,10 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                 .FindMethod( "BindClass", IDisposable, false, IStyledElement,
                 cfg.WellKnownTypes.String,
                 IBinding, cfg.WellKnownTypes.Object);
+
+            IBrush = cfg.TypeSystem.GetType("Avalonia.Media.IBrush");
+            ImmutableSolidColorBrush = cfg.TypeSystem.GetType("Avalonia.Media.Immutable.ImmutableSolidColorBrush");
+            ImmutableSolidColorBrushConstructorColor = ImmutableSolidColorBrush.GetConstructor(new List<IXamlType> { UInt });
         }
     }