Hi , 

Why don't you do it from code behind of OtherColor.aspx. This code works fine for me .

using System.Drawing;
public partial class Default4 : System.Web.UI.Page
{
    protected string strColor;
    protected void Page_Load(object sender, EventArgs e)
    {

        strColor = Server.UrlDecode(Request.QueryString["Data"]);
        Label1.BackColor = Color.FromName(strColor);
    }
}