Gold's ductility, malleability, rich color, and purity are what allowed goldsmiths thousands of years ago to make it into jewelry. It can be alloyed into several colors, including pink, yellow, and white.

High quality white gold is alloyed with palladium and is hypo-allergenic. Nickel white golds are less durable and should not be used in white gold engagement rings, especially if prong setting a diamond.

Most women under 35 prefer white gold over yellow gold in an engagement ring, but trust your own judgement. If you have an incling in any particular direction, go with it. You know your girlfriend best.