The decision to buy either yellow gold or white gold is most often decided by a preference for one metallic hue over the other. Some people prefer the cooler shade of silver over the warmer yellow gold.
With the price of gold rising quite dramatically in recent times, those who would normally have chosen white gold are beginning to look more closely at a 925 silver necklace as an alternative. Silver is almost indistinguishable to white gold in looks but it can be subject to tarnishing. Rhodium plating can be used to prevent this from happening in the same way that most white gold is also rhodium plated.
It isn’t cheap to have done and needs to be re-plated every 12 or 18 months depending upon how often the jewellery is worn. In any event it is still going to be significantly cheaper to buy a silver necklace than a similar white gold necklace.