using System;

using System.Xml;

public class Program

{

    public static void Main()

    {

        var content = @"<?xml version=""1.0"" encoding=""UTF-8""?>

<MyRootElement xmlns=""urn:MyNamespaceUri_1"">

  <Color>

    <Name>Primary</Name>

    <ID>1</ID>

    <Description>Red</Description>    

    <Status>In Use</Status>    

    <Reference xmlns=""urn:MyNamespaceUri_2"">

      <ColorCode>3</ColorCode>      

      <ID>1616</ID>

    </Reference>

  </Color>

</MyRootElement>";

        XmlDocument doc = new XmlDocument();            

        doc.LoadXml(content);

​

        var nsmgr = new XmlNamespaceManager(doc.NameTable);

        nsmgr.AddNamespace("ns1", "urn:MyNamespaceUri_1");

        nsmgr.AddNamespace("ns2", "urn:MyNamespaceUri_2");

​

        XmlNode testNode = doc.SelectSingleNode("/ns1:MyRootElement/Color/ns2:Reference/ID", nsmgr);

        if (testNode != null)

        {

           Console.WriteLine(testNode.InnerText);

        }

    }

}