Wow white gold is so not real gold but a mixture of other metals to form a white so called gold which really just is yellow gold. The purity of course is now not pure and although depending on what other metals are used, often Nickel, Palladium, Platnium, and Manganese.
White gold does have yellow true gold and does often have enough parts gold to still be in the 14k range but it’s not more expensive than pure 18k or 24k gold.
White gold is probably the most popular of the alloys in terms of jewelry and engagement rings. Although it’s impossible without testing to see how much white gold or gold is within an object. It’s important to always inquire about the parts per gold ratio in the white gold piece. The highest is around 18k for white gold. Often rhodium is used as a whitener as white gold itself is often yellowing as time goes on.
Platinum and Nickel can increase the whiteness of the object and also is skin safe, it also is more exspensive than gold so depending on how much is used this can increase the value of the jewelry.
Pure gold is yellow and is 24karat or 24 parts of AU. All colored golds are going to be less than that and although the design or piece of jewelry may hold demand or intrinsic value. The safest investment would still be by weight a pure minted gold from a certifiable refinery that holds all good faith practice and audit reports on hand.