We picked them out together, and we both have white gold because we thought it was easier to match with anything (More her idea LOL) So white may be the safe bet. I just posted both to look at.
One thing I've learned being married for almost 7 years now is to just let her pick which one she wants. Or better yet just give her the option of picking whatever it is she wants for a gift and giving her the money, because there is always something a woman has her eye on. Also a little aside but you're not actually getting two grams of gold with either necklace the purity is only 14k so 14/24 = 58.33% in actual gold weight.
I don't think it is gauche to mix gold colors, as long as they aren't right next to each other. In other words, a white gold ring and a yellow gold necklace is fine; but not a white gold ring near a yellow gold bracelet. At least in my book. But won't a 2 gram chain be super thin and delicate? I could see the thing breaking pretty easily - especially if 18K.