I have seen this question asked a great many times and there seems to be great confusion regarding what white gold actually is. To set the record straight, gold is gold is gold is yellow. There is no such thing as white gold as a metal, rather the gold alloy is white when pure 24 karat gold is mixed with white metals such as silver, nickel, palladium and platinum. The same applies to rose gold with copper and red metals and other colors of gold (gold alloys have been made in blue, purple, green, black and more).
18k white gold is therefore 75% (18 of 24) pure gold, which is yellow, and 25% white metals.
14k white gold is 58.5% (14 of 24) pure gold and 41.5% white metals.
And so on…
This means of course that despite 18k gold being more expensive (and more valuable of course), it is in fact whiter due to there being more white metals in the alloy. The main advantage of this is with the rhodium plating. Most white gold jewelry is plated with an even whiter metal called rhodium, which will give that dazzling shiny finish that we all love. The trouble is, the more yellow the gold alloy is, the more obvious it becomes when the rhodium starts to wear off (which it will do). This isn't a big deal and any piece can be re-dipped in rhodium for a small fee, but it can be rather inconvenient or disheartening if you don't know why your white gold ring has suddenly turned yellow!
It isn't recommended to choose 10k and 9k gold as the purity of gold in the alloy is so low that you may as well purchase silver. If you have any allergies, they may show with 10k and 9k gold. Also due to the low purity, the metal will be "dirty" which can cause stains in the metal, black marks and pitfalls that will show over time.
