Change a dynamically created pictureboxes backcolor

private void PieceClick(object sender, EventArgs e)
{
    RefressChessBoard();

    //Get the properties of the picturebox selected
    CurrentPiece = (PictureBox)sender;

    if (PieceMove)
    {
        foreach (PictureBox chessPiece in AllPieces)
	{
	    chessPiece.BackColor = Color.Transparent;
	    chessPiece.Visible = false;
	}
    }
    if (!PromotePawn)
    {
        //get the x coordinate  of the selected piece
	FromX = CurrentPiece.Left / 100;
	FromX = Convert.ToInt32(Math.Floor(FromX));

	//get the y coordinate of the selected piece
	FromY = CurrentPiece.Top / 100;
	FromY = Convert.ToInt32(Math.Floor(FromY));
 
	if (chessEngine.isPlayerPiece((byte)FromX, (byte)FromY))
	{
	     //Get the Piece that was selected
	     PieceSelected = chessEngine.CurrentBoard.GetPieceAtPosition((byte)FromX, (byte)FromY);

	     //Check if the player selected a pawn
	     if (CurrentPiece.Name == enPieceType.WhitePawn.ToString() || CurrentPiece.Name == enPieceType.BlackPawn.ToString())
             {
		  PossibleMoves = chessEngine.GetMoves((byte)FromX, (byte)FromY);
		  CurrentPiece.BackColor = Color.OliveDrab;
		  PieceMove = true;
	     }

	     DisplayAllPossibleMoves();
	}
}