Fixes #2834. v1 Border BorderBrush and Background wrongly sets to an invalid Color enum.

Terminal.Gui/Core/Border.cs

@@ -375,8 +375,10 @@ namespace Terminal.Gui {
 		public Color BorderBrush {
 			get => borderBrush != null ? (Color)borderBrush : (Color)(-1);
 			set {
-				borderBrush = value;
-				OnBorderChanged ();
+				if (Enum.IsDefined (typeof (Color), value)) {
+					borderBrush = value;
+					OnBorderChanged ();
+				}
 			}
 		}
 
@@ -386,8 +388,10 @@ namespace Terminal.Gui {
 		public Color Background {
 			get => background != null ? (Color)background : (Color)(-1);
 			set {
-				background = value;
-				OnBorderChanged ();
+				if (Enum.IsDefined (typeof (Color), value)) {
+					background = value;
+					OnBorderChanged ();
+				}
 			}
 		}
 
@@ -445,12 +449,10 @@ namespace Terminal.Gui {
 
 		private void Parent_Removed (View obj)
 		{
-			if (borderBrush != null)
-			{
+			if (borderBrush != null) {
 				BorderBrush = default;
 			}
-			if (background != null)
-			{
+			if (background != null) {
 				Background = default;
 			}
 			child.Removed -= Parent_Removed;

UnitTests/Core/BorderTests.cs

@@ -619,5 +619,29 @@ At 0,0
 ████████████████████
 At 0,4              ", output);
 		}
+
+		[Fact]
+		public void BorderBrush_Background_Only_Is_Set_To_Valid_Color_Enum ()
+		{
+			var border = new Border ();
+			Assert.Equal ((Color)(-1), border.BorderBrush);
+			Assert.Equal ((Color)(-1), border.Background);
+			Assert.Null (border.GetFieldValue<string> ("borderBrush"));
+			Assert.Null (border.GetFieldValue<string> ("background"));
+
+			border.BorderBrush = (Color)(-1);
+			border.Background = (Color)(-1);
+			Assert.Equal ((Color)(-1), border.BorderBrush);
+			Assert.Equal ((Color)(-1), border.Background);
+			Assert.Null (border.GetFieldValue<Color?> ("borderBrush"));
+			Assert.Null (border.GetFieldValue<Color?> ("background"));
+
+			border.BorderBrush = Color.Blue;
+			border.Background = Color.White;
+			Assert.Equal (Color.Blue, border.BorderBrush);
+			Assert.Equal (Color.White, border.Background);
+			Assert.Equal (Color.Blue, border.GetFieldValue<Color> ("borderBrush"));
+			Assert.Equal (Color.White, border.GetFieldValue<Color?> ("background"));
+		}
 	}
 }

UnitTests/ReflectionTools.cs

@@ -32,4 +32,12 @@ public static class ReflectionTools {
 		}
 		return null;
 	}
+
+	public static T GetFieldValue<T> (this object obj, string name)
+	{
+		// Set the flags so that private and public fields from instances will be found
+		var bindingFlags = BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance;
+		var field = obj.GetType ().GetField (name, bindingFlags);
+		return (T)field?.GetValue (obj);
+	}
 }