In order to have an electron absorb a photon the electron has to go to a higher shell in one of the ions. This takes a lot of energy and is typically more than the energy of photons in visible light. Hence there is no absorption of visible light and these materials are transparent. Using the same ingredients as above we can calculate the energy and frequency of the motion of the ion pairs. This is typically in the infrared.
Ionic solids dissolve in water.
The polar water moleculre likes to squeeze in between an ion pair and seperate them.