The kanji for "Shirogane" (白金) literally mean "white gold," although this term actually refers to silver (or platinum if you pronounce it as "hakkin"; white gold is just "ホワイトゴールド"); there's actually a "Shirokane" in Tokyo. Kugane (黄金), on the other hand, is an older term that refers to gold (the kanji literally mean "yellow gold"). In terms of culture, I think that it is quite obvious for anyone who knows anything about Japan that Kugane is supposed to be FFXIV's take on Kyoto. The fact that there are people dressed in traditional Japanese garb should give it away, but that weren't enough, the quests there (e.g., the geiko stuff you mentioned) should be enough to solidify that conclusion. The really telling point is the whole "Sekiseigumi" thing - this is clearly a play on the "Shinsengumi" which famously patrolled the streets of Kyoto during the Bakumatsu era and, among other things, prevented the city from being set on fire in connection with the Ikedaya incident.