CICLOPS has released this low resolution view of Tethys. This image highlights albedo variations seen on the surface of this satellite particularly seen at infrared wavelengths. This image was taken last month a few days after the first non-targeted encounter of Tethys and has a resolution of 8 km/pixel.
Update 04/22/2005 12:00pm - Found a great Voyager 1 image showing this dark band. According to the caption for that image:
The exact cause for the dark band is unknown, but a possible interpretation comes from recent Galileo images of Jupiter's moons Ganymede and Callisto. Both satellites exhibit light polar caps that are made from bright ice deposits on pole-facing slopes of craters. From a distance the caps appear brighter due to a haze caused by thousands of unresolved patches of ice in small craters. The dark band on Tethys may have been formed in a similar manner, consisting of hazy polar caps of unresolved bright ice patches with a dark zone in-between.