1 uses
 2   Winapi.CommCtrl,
 3   Vcl.Styles,
 4   Vcl.Themes,
 5   uxTheme;
 6 
 7 Procedure SetVclStylesColorsCalendar( DateTimePicker: TDateTimePicker);
 8 Var
 9   LTextColor, LBackColor : TColor;
10 begin
11    uxTheme.SetWindowTheme(DateTimePicker.Handle, '', '');//disable themes in the calendar
12    //get the vcl styles colors
13    LTextColor:=StyleServices.GetSystemColor(clWindowText);
14    LBackColor:=StyleServices.GetSystemColor(clWindow);
15 
16    DateTimePicker.Color:=LBackColor;
17    //set the colors of the calendar
18    DateTimePicker.CalColors.BackColor:=LBackColor;
19    DateTimePicker.CalColors.MonthBackColor:=LBackColor;
20    DateTimePicker.CalColors.TextColor:=LTextColor;
21    DateTimePicker.CalColors.TitleBackColor:=LBackColor;
22    DateTimePicker.CalColors.TitleTextColor:=LTextColor;
23    DateTimePicker.CalColors.TrailingTextColor:=LTextColor;
24 end;
25 
26 procedure TForm2.DateTimePicker1DropDown(Sender: TObject);
27 var
28   hwnd: WinAPi.Windows.HWND;
29 begin
30   hwnd := SendMessage(TDateTimePicker(Sender).Handle, DTM_GETMONTHCAL, 0,0);
31   uxTheme.SetWindowTheme(hwnd, '', '');//disable themes in the drop down window
32 end;
33 procedure TForm2.FormCreate(Sender: TObject);
34 begin
35   SetVclStylesColorsCalendar(DateTimePicker1);
36 end;