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;