Code:

function DesktopColor(const X, Y: Integer): TColor;

var

  c: TCanvas;

begin

  c := TCanvas.Create;

  try

    c.Handle := GetWindowDC(GetDesktopWindow);

    Result   := GetPixel(c.Handle, X, Y);

  finally

    c.Free;

  end;

end;

procedure TForm1.Timer1Timer(Sender: TObject);

var

  Pos: TPoint;

begin

  GetCursorPos(Pos);

  Panel1.Color := DesktopColor(Pos.X, Pos.Y);

end;