The appearance of the sandwich is controlled by how it was grilled, what it was made from and how it is presented.  The main reason for toasting a panini with an electric press or a grill pan is to create clearly defined grill marks and ridges on the bread.  While the grill marks are visually appealing they are not what make the sandwich great.To increase the attractiveness of the sandwich consider how it will be presented.  A whole sandwich served by itself on a plate is not nearly as attractive as one sliced on a diagonal and served with garnishes.  If the sandwich is to be served sliced in half, take the time to think about what the middle of the sandwich looks like.  If you are using a white meat suck as chicken or turkey add some color by using a yellow cheese or colorful vegetables such as roasted red peppers.