procedure ShadeIt(f: TForm; c: TControl; Width: Integer; Color: TColor);
var
  rect: TRect;
  old: TColor;
begin
  if (c.Visible) then
  begin
    rect := c.BoundsRect;
    rect.Left := rect.Left + Width;
    rect.Top := rect.Top + Width;
    rect.Right := rect.Right + Width;
    rect.Bottom := rect.Bottom + Width;
    old := f.Canvas.Brush.Color;
    f.Canvas.Brush.Color := Color;
    f.Canvas.fillrect(rect);
    f.Canvas.Brush.Color := old;
  end;
end;

// Пример использования:

procedure TForm1.FormPaint(Sender: TObject);
var
  i: Integer;
begin
  for i := 0 to Self.ControlCount - 1 do
    ShadeIt(Self, Self.Controls[i], 3, clBlack);
end;