Added handling of invalid color as default color

- adapted test to check for default value
- see svg-net#399

Source/External/ExCSS/Parser.Blocks.cs

@@ -554,10 +554,13 @@ private bool ParseSingleValueHexColor(string color)
         {
             HtmlColor htmlColor;
 
-            if(HtmlColor.TryFromHex(color, out htmlColor))
+            if (HtmlColor.TryFromHex(color, out htmlColor))
                 return AddTerm(htmlColor);
-
-            return false;    
+            else
+                // the value is invalid - remove the property to use the default value
+                RemoveCurrentProperty();
+
+            return true;    
         }
 
         #region Namespace

Tests/Svg.UnitTests/LexerIssueTests.cs

@@ -62,8 +62,29 @@ public void Lexer_NoImportantAndImportantAfterNonHex_Success()
         [TestMethod]
         public void Lexer_FileWithInvalidHex_ColorTagIsIgnored()
         {
-            Assert.Inconclusive("This test fails due to a lexer error");
-            GenerateLexerTestFile("color: #0046;");
+            // valid colors
+            var doc = GenerateLexerTestFile("fill: #ff0000; stroke: #ffff00");
+            var path = doc.GetElementById<SvgPath>("path1");
+            Assert.AreEqual(System.Drawing.Color.Red, ((SvgColourServer)path.Fill).Colour);
+            Assert.AreEqual(System.Drawing.Color.Yellow, ((SvgColourServer)path.Stroke).Colour);
+
+            // invalid/valid color combinations - default color is used for each invalid color
+            doc = GenerateLexerTestFile("fill: #ff00; stroke: #00ff00");
+            path = doc.GetElementById<SvgPath>("path1");
+            // default fill color is Black
+            Assert.AreEqual(System.Drawing.Color.Black, ((SvgColourServer)path.Fill).Colour);
+            Assert.AreEqual(System.Drawing.Color.Lime, ((SvgColourServer)path.Stroke).Colour);
+
+            doc = GenerateLexerTestFile("fill: #fff; stroke: 005577");
+            path = doc.GetElementById<SvgPath>("path1");
+            Assert.AreEqual(System.Drawing.Color.White, ((SvgColourServer)path.Fill).Colour);
+            // default stroke color is null (transparent)
+            Assert.IsNull(path.Stroke);
+
+            doc = GenerateLexerTestFile("fill:; stroke: #00557;");
+            path = doc.GetElementById<SvgPath>("path1");
+            Assert.AreEqual(System.Drawing.Color.Black, ((SvgColourServer)path.Fill).Colour);
+            Assert.IsNull(path.Stroke);
         }
 
         /// <summary>