[X] My Assistant

[David]

Most of Saturn's nine largest moons have some characteristic that distinguishes them from the others, by which I can more or less instantly recognize them when I see their images:
Titan is big, orange, and smoggy
Iapetus is pied black and white, with an immense crater, irregular shape, and that wacky equatorial ridge (almost too many weirdnesses for one moon!)
Enceladus is small, icy, and smooth like a spherical hockey rink, with those warm antarctic catscratches
Mimas is small, bumpy, egg-round, with a really big crater
Hyperion is irregular and pocked full of medium-sized black-bottomed holes
Phoebe is potato-shaped with a less dense pocking of conical craters, plus a few larger ones

But the three I still have a lot of trouble distinguishing are Rhea, Dione, and Tethys. I know Rhea is considerably larger, but the scale difference isn't enough to make it a lot less lumpy than the other two, so that doesn't help much. What distinguishing marks should I look for to be able to easily differentiate these three moons?