Unset colors are now parsed correctly, color properties have optional colors

src/DotTiled.Tests/TestData/Maps/map-with-common-props/map-with-common-props.cs

@@ -57,7 +57,8 @@ public partial class TestData
       new FloatProperty { Name = "floatprop", Value = 4.2f },
       new IntProperty { Name = "intprop", Value = 8 },
       new ObjectProperty { Name = "objectprop", Value = 5 },
-      new StringProperty { Name = "stringprop", Value = "This is a string, hello world!" }
+      new StringProperty { Name = "stringprop", Value = "This is a string, hello world!" },
+      new ColorProperty { Name = "unsetcolorprop", Value = Optional<Color>.Empty }
     ]
   };
 }

src/DotTiled.Tests/TestData/Maps/map-with-common-props/map-with-common-props.tmj

@@ -58,6 +58,11 @@
          "name":"stringprop",
          "type":"string",
          "value":"This is a string, hello world!"
+        }, 
+        {
+         "name":"unsetcolorprop",
+         "type":"color",
+         "value":""
         }],
  "renderorder":"right-down",
  "tiledversion":"1.11.0",

src/DotTiled.Tests/TestData/Maps/map-with-common-props/map-with-common-props.tmx

@@ -8,6 +8,7 @@
   <property name="intprop" type="int" value="8"/>
   <property name="objectprop" type="object" value="5"/>
   <property name="stringprop" value="This is a string, hello world!"/>
+  <property name="unsetcolorprop" type="color" value=""/>
  </properties>
  <layer id="1" name="Tile Layer 1" width="5" height="5">
   <data encoding="csv">