My Kallah seems to be interested in "white gold", but one jeweler told me that white gold is plated. Is this correct? If it is not plated, is white gold permissible? Also, how many "Karats" should the gold be? 14 karats is 58.5% gold and 18 karats is 75% gold. 24 karats is still less than 100%, but the metal is too soft for use as jewelery. Is there an online reference where I can learn more about the Halachah of the ring... and for the wedding ceremony?

Mazal Tov. The ring can be of any valuable metal though traditionally it will be gold. (According to kabalistic sources it's better to be silver) It can therefore be white or yellow gold and of any purity you wish. You should make sure that your Kallah knows it's material and value before the wedding. Don't know of an online reference but you can try any of the Jewish portals or search engines.