A rare view of Io and the small moon Amalthea seen in the same view was taken by Galileo and recently reprocessed by Ted Stryk (his page is linked lower right). Amalthea is a tiny elongated moon that appears to be quite red. It is assumed that the longish shape and red hue come from the deposit of materials ejected off Io and spiral inward to Jupiter, swept up by Amalthea in its orbital path.
A similar phenomenon has also been seen at Saturn with moonlets that “sweep” ring materials.