const
  WM_DATECHANGED = WM_USER 200;
type
  TForm1 = class(TForm)
    MonthCalendar1: TMonthCalendar;
    procedure MonthCalendar1GetMonthInfo(Sender: TObject; Month: Cardinal;
      var MonthBoldInfo: Cardinal);
  private
    procedure WMDATECHANGED(Var Msg:TMessage);Message WM_DATECHANGED;
  public
    { Public declarations }
  end;    var
  Form1: TForm1;    implementation    {$R *.DFM}    procedure TForm1.MonthCalendar1GetMonthInfo(Sender: TObject;
  Month: Cardinal; var MonthBoldInfo: Cardinal);
begin
  PostMessage(Handle,WM_DATECHANGED,0,0);
end;    procedure TForm1.WMDATECHANGED(Var Msg:TMessage);
var
  Year, Month, Day: Word;
begin
  DeCodeDate(MonthCalendar1.Date,Year,Month,Day);      With MonthCalendar1.CalColors do
    Case Month of
      1 :MonthBackColor := ClNavy;
      2 :MonthBackColor := ClYellow;
      3 :MonthBackColor := ClWhite;
      4 :MonthBackColor := ClBlue;
      .....
      12:MonthBackColor := ClRed;
    end;
end;