Ok, first things first. There is no white gold naturally formed. Gold can be found in green, pink and yellows, due to the mineral influence around it, but never white. Alloying yellow gold with a combination of silver, palladium, copper, and/or zinc makes white gold. Nickel is no longer regularly added due to allergic reactions of many people.
White gold will tarnish quicker than sterling silver! Due to the alloys present to make the 'white' color, white gold needs to be coated with rhodium to prevent tarnish. The rhodium will eventually wear off and the piece will then need to be professionally re-plated.
From my personal experience, I have made pieces using 14kt white gold wire, because a customer simply "had to have" 14k white gold. Because this white gold wire would need to be plated with rhodium after creating the design, and the stone wouldn't be protected, it went "bare" and turned black within a few weeks! She has since had me redo all of these pieces using Argentium.
In conclusion, if you or your customer desires a really white metal that will stay bright for a long time, use Argentium silver. If they have a 14kt white gold "ego" issue, save yourself the aggravation and future headaches by being honest with them about what "white gold" really is.
Answer contributed by Dale "Cougar" Armstrong