Like Saturn's blue ring, it probably owes its existence to an accompanying small moon. Scientists suggest that subtle forces acting on dust in the rings allow smaller particles to persist, while larger ones are recaptured by the moon. These smaller particles reflect blue light, giving the rings their distinctive color.
All other rings -- those around Jupiter, Saturn, Uranus and Neptune -- are made up of both large and small particles, making the rings reddish in appearance.
The BBC has more here.