var 

  OldColor: TColor; 
  Element: TColor = COLOR_BTNFACE; 

  {....} 

{ 
  Set the color for a system element. SetSysColors function 
  changes the current Windows session only. 
  The new colors are not saved when Windows terminates. 
  For a list of color elements see  Win32 API Help - Function GetSysColor 


  Open the ColorDialog - and set the new color systemwide 
} 

procedure TForm1.Button1Click(Sender: TObject); 
begin 
  if ColorDialog1.Execute then 
  begin 
    SetSysColors(1, Element, ColorDialog1.Color); 
  end; 
end; 

{ 
  Save the old color value of the element COLOR_BTNFACE to restore on Button2 click 
} 

procedure TForm1.FormShow(Sender: TObject); 
begin 
  OldColor := GetSysColor(COLOR_BTNFACE); 
end; 

{ 
  Restore the old color value 
  Stellt den alten Farbwert wieder her 
} 

procedure TForm1.Button2Click(Sender: TObject); 
begin 
  SetSysColors(1, Element, OldColor); 
end;