The following example demonstrates drawing transparent text on the canvas of a TBitmap.

Example:
procedure TForm .Button Click(Sender: TObject);
var
  OldBkMode : integer;
begin
  Image .Picture.Bitmap.Canvas.Font.Color := clBlue;
  OldBkMode := SetBkMode(Image .Picture.Bitmap.Canvas.Handle,
                         TRANSPARENT);
  Image .Picture.Bitmap.Canvas.TextOut( 0,  0, 'Hello');
  SetBkMode(Image .Picture.Bitmap.Canvas.Handle,
            OldBkMode);
end;