This question comes up frequently, at parties and at online Q&A sites. The answer is simple: absolutely not. Karat for karat white gold and yellow gold have exactly the same gold content and therefore exactly the same value.
To understand fully it is useful to know what makes white gold white. To begin, there is no such thing in nature as “white gold” since gold itself is an element which, in its pure form, is yellow. When we make jewellery we first “water down” the pure gold into an alloy by adding other metals. These alloys are known as “karat gold” and come in various standardized purities like 18 karat (75% gold) or 14 karat (58.5% gold). See the article on Karat Gold for a more complete discussing of the subject.
The other metals added to gold to make an alloy affect various properties of the metal, including the colour. To make a white gold we add either nickel or palladium. Nickel is more common in North America and produces quite a bright white gold that is very hard and very useful for work like setting stones because it is highly resistant to bending and therefore dropping the stone! In Europe it is more common to use palladium as the alloy to make a white gold. Palladium produces a softer white that looks “grey” to the North American eye. For this reason jewellery made with a palladium white gold is often “colour plated” with another metal, rhodium, to give it a bright finish more pleasing to North American taste.
In any event, an 18 karat yellow gold, an 18 karat nickel white and an 18 karat palladium white all contain the same 75% gold content and are all worth exactly the same amount.More Technical Information About Precious Metals