The RichTextBox Control is transparent to the background.

Http://www.codeproject.com/cs/miscctrl/TransparentTextBox.asp
How to make the RichTextBox Control transparent: After transparency, you can set the background image on the back, but it is usually shaking.
There are also other ways to set transparency and use the timer to refresh, as shown below:
Http://www.codeproject.com/cs/miscctrl/AlphaBlendedTextControls.asp

RichTextBox

<span class="cs-keyword">class</span> TransparentControl : Control{ <span class="cs-keyword">public</span> TransparentControl() { <span class="cs-keyword">base</span>.SetStyle( ControlStyles.UserPaint, <span class="cs-keyword">true</span> ); <span class="cs-keyword">base</span>.SetStyle( ControlStyles.DoubleBuffer, <span class="cs-keyword">true</span> ); <span class="cs-keyword">base</span>.SetStyle( ControlStyles.SupportsTransparentBackColor, <span class="cs-keyword">true</span> ); }} <span class="cs-keyword">class</span> TransparentRichTextBox : RichTextBox{ <span class="cs-keyword">public</span> TransparentRichTextBox() { <span class="cs-keyword">base</span>.ScrollBars = RichTextBoxScrollBars.None; }  <span class="cs-keyword">override</span> <span class="cs-keyword">protected</span> CreateParams CreateParams { <span class="cs-keyword">get</span> { CreateParams cp = <span class="cs-keyword">base</span>.CreateParams; cp.ExStyle |= <span class="cs-literal">0x20</span>; <span class="cs-keyword">return</span> cp; } }  <span class="cs-keyword">override</span> <span class="cs-keyword">protected</span> <span class="cs-keyword">void</span> OnPaintBackground( PaintEventArgs e ) { }}

Textbox collapse

public class TransparentTextBox : TextBox{   PictureBox pictureBox = new PictureBox();   public TransparentTextBox()   {      pictureBox.Dock = DockStyle.Fill;      this.Controls.Add( pictureBox );    }   protected override void WndProc( ref Message m )   {      base.WndProc( ref m );      switch( m.Msg )      {         case Win32.WM_PAINT:            Bitmap bmpCaptured =               new Bitmap( this.ClientRectangle.Width, this.ClientRectangle.Height );            Bitmap bmpResult =               new Bitmap( this.ClientRectangle.Width,this.ClientRectangle.Height );            Rectangle r =               new Rectangle( 0, 0, this.ClientRectangle.Width,               this.ClientRectangle.Height );             CaptureWindow( this, ref bmpCaptured );             this.SetStyle( ControlStyles.SupportsTransparentBackColor, true );            this.BackColor = Color.Transparent;            ImageAttributes imgAttrib = new ImageAttributes();            ColorMap[] colorMap = new ColorMap[ 1 ];            colorMap[ 0 ] = new ColorMap();            colorMap[ 0 ].OldColor = Color.White;            colorMap[ 0 ].NewColor = Color.Transparent;            imgAttrib.SetRemapTable( colorMap );             Graphics g = Graphics.FromImage( bmpResult );            g.DrawImage( bmpCaptured, r, 0 , 0, this.ClientRectangle.Width,                 this.ClientRectangle.Height, GraphicsUnit.Pixel, imgAttrib );            g.Dispose();            pictureBox.Image = ( Image )bmpResult.Clone();          break;         case Win32.WM_HSCROLL:         case Win32.WM_VSCROLL:            this.Invalidate(); // repaint           // if you use scrolling then add these two case statements         break;   }}private static void CaptureWindow( Control control, ref Bitmap bitmap ){   Graphics g = Graphics.FromImage( bitmap );   int i = ( int )( Win32.PRF_CLIENT | Win32.PRF_ERASEBKGND );   IntPtr iPtr = new IntPtr( 14 );   IntPtr hdc = g.GetHdc();   Win32.SendMessage( control.Handle, Win32.WM_PRINT, hdc, iPtr );    g.ReleaseHdc( hdc );   g.Dispose();}