Jewels in white gold may tend with time to turn yellow. It is a well-known phenomenon, characteristic of white gold alloys, that in some cases may be accelerated by reactions to external agents. However, since it is only on the surface, it can be avoided or easily overcome by periodical cleaning with purpose-made products.
However, if the jewel is rhodium-plated, the yellowing may be the result of the loss of lustre of the cold component of the rhodium-plating process and thus the emerging of the warmer colour, characteristic of the natural white gold alloy.
In any case, also rhodium-plating is a surface treatment that can be easily restored.