White gold (whether 14Kt or 18Kt) has been rendered white by the addition of different alloys that whiten/bleach gold. There aren't many elements that will make gold white. The most effective is nickel, however many in the population are showing a sensitivity to nickel. The next best is palladium, a platinum group precious metal. Platinum will also whiten gold but you need a lot of it. Palladium and platinum are expensive so many people still use nickel to make white gold.

The word "white" can be very subjective and relative. White gold is whiter than yellow gold. However, many times white gold looks dull gray or "dirty" when compared to platinum and silver. This is why many people plate white gold with Rhodium. It is very white and bright and appealing to the eye! It is also very hard. Actually the brightest and whitest metal is silver. But people don't silver plate because it is soft and will tarnish. Rhodium is the next brightest metal, doesn't tarnish and is a platinum group metal, and a very expensive one at that, running about 1700.00 per ounce! This is why many people put a very thin coating that will need replating after a few years. Good quality plating should be bright and stain free. Plating will not hide scratches, dents and so forth. If you replate a dull scratchy item, you will get a dull scratchy plating

 

The thicker the plating, the more durable it will be. Any Rhodium plating that is at least 90-100 microinches will be extremely durable. In addition, the plating will COVER the base metal completely. People who have 18KT white gold rings that only have a 20 microinch coating are eventually going to see the base metal color "bleed through" as the plating wears or oxidizes over time.