Many contemporary jewelry items especially those made of white gold, are electroplated in rhodium to enhance shine and durability.
Sometimes, platinum or silver jewelry is rhodium-plated. In the case of platinum, it is because rhodium is a bit brighter than platinum, so it is used to enhance the shine. For silver, it is a little bit different. Silver is actually more reflective (shinier) than rhodium, but silver is also a much softer metal, and can be scratched very easily. So the owner of a rhodium-plated silver piece is trading a small bit of shine for a longer, scratch-free life.