Starting values of colors is "Empty"

EduNetworkBuilder/NetworkBuilder.cs

@@ -108,6 +108,8 @@ namespace EduNetworkBuilder
                 cbFillColor.Items.Add(ColorName);
                 cbLineColor.Items.Add(ColorName);
             }
+            cbFillColor.Text = "Empty";
+            cbLineColor.Text = "Empty";
 
             BuildButtons();
             LayoutButtons();