Image service sublayers are sometimes drawn with no color (no fill color, no outline color) because the service author wants to use them to provide labels for another layer. However, they are shown in the ArcMap table of contents as a polygon symbol with a solid outline. This may cause confusion when looking for these polygons on the map, as one might expect to see them with a solid outline. In fact, they have been defined with no color outline and are rendered correctly on the map.
This problem has been resolved for ArcGIS 8.1.2.