You can change the colors, borders, font styles by editing MagicZoom.css file. It is located in /content/skins/*/javascript/ .  These are the 3 classes you can change:

/* CSS class for zoomed area */
.MagicZoomBigImageCont {
border: 1px solid #9e2f2d;
}

/* Header look and feel CSS class */
/* header is shown if "title" attribute is present in the <a> tag */
.MagicZoomHeader {
font: 10px Tahoma, Verdana, Arial, sans-serif;
color: #fff;
background: #9e2f2d;
text-align: center;
}

/* CSS class for small looking glass square under mouse */
.MagicZoomPup {
border: 1px solid #aaa;
background: #fff;
}