White gold is a mixture of yellow gold and white metals that give it a white appearance. Platinum is a naturally white metal. Both precious metals are perfectly suited for jewellery: non tarnishing, non-allergenic, and capable of being intricately worked.
The price difference is subject to market fluctuation; however, platinum is heavier, and there is a higher labour component in the finishing costs.
White gold is normally finished with rhodium plating. When this wears off, white gold may show a feint tinge of yellow. Polishing and replating will restore the finish to original condition.