How to display user conrtol on any form with dim background c#

i am working with C# v2.0 winform apps. i want to show user control on top of another form with dim background or semi transparent background whose mdiparent property has been assign. i wrote a code which works fine but when i am showing from a form which has mdiparent then background become full black instead of specifying opacity .5. here i will post my code. please have a look and tell me how could i show my user control with semi transparent background instead of full black.

here is my code

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace reman
{publicpartialclassMaskedDialog:Form{staticMaskedDialog mask;staticForm frmContainer;privateForm dialog;privateUserControl ucDialog;privateMaskedDialog(Form parent,Form dialog){this.dialog = dialog;this.FormBorderStyle=FormBorderStyle.None;this.BackColor=System.Drawing.Color.Black;this.Opacity=0.50;this.ShowInTaskbar=false;this.StartPosition=FormStartPosition.Manual;this.Size= parent.ClientSize;this.Location= parent.PointToScreen(System.Drawing.Point.Empty);
            parent.Move+=AdjustPosition;
            parent.SizeChanged+=AdjustPosition;}privateMaskedDialog(Form parent,UserControl ucDialog){this.ucDialog = ucDialog;this.FormBorderStyle=FormBorderStyle.None;this.BackColor=System.Drawing.Color.Black;this.Opacity=0.50;this.ShowInTaskbar=false;this.StartPosition=FormStartPosition.Manual;this.Size= parent.ClientSize;this.Location= parent.PointToScreen(System.Drawing.Point.Empty);
            parent.Move+=AdjustPosition;
            parent.SizeChanged+=AdjustPosition;}privatevoidAdjustPosition(object sender,EventArgs e){Form parent = sender asForm;this.Location= parent.PointToScreen(System.Drawing.Point.Empty);this.ClientSize= parent.ClientSize;}publicstaticDialogResultShowDialog(Form parent,Form dialog){
            mask =newMaskedDialog(parent, dialog);
            dialog.StartPosition=FormStartPosition.CenterParent;
            mask.Show();DialogResult result = dialog.ShowDialog(mask);
            mask.Close();return result;}publicstaticDialogResultShowDialog(Form parent,UserControl dialog){
            mask =newMaskedDialog(parent, dialog);
            frmContainer =newForm();
            frmContainer.ShowInTaskbar=false;
            frmContainer.FormBorderStyle=System.Windows.Forms.FormBorderStyle.None;
            frmContainer.StartPosition=FormStartPosition.CenterParent;
            frmContainer.Height= dialog.Height;
            frmContainer.Width= dialog.Width;

            frmContainer.Controls.Add(dialog);
            mask.MdiParent= parent.MdiParent;
            mask.Show();DialogResult result = frmContainer.ShowDialog(mask);
            frmContainer.Close();
            mask.Close();return result;}publicstaticvoidCloseDialog(){if(frmContainer !=null){
                frmContainer.Close();}}}}

the way i am calling my MaskedDialog form from another form.

privatevoid btnAct_Click(object sender,EventArgs e){
    ucCheckInfo ucInfo =new ucCheckInfo();MaskedDialog.ShowDialog(this, ucInfo);}

can any one rectify my code as a result background should be semi-transparent. thanks