[1] - Ajwebat al-Istiftaat (Farsi Answers to Religious Queries), pg.90, Tawzih al-Masail (with annotations by Imam Khomeini), vol.2, pg. 927, issue No.443. Grand Ayatollah Khamenei: If a metal is called white gold, it is in fact the yellow gold which becomes white when a white metal is blended with it; therefore it is haram. In case, however, there is so little gold in it that it is not considered to be gold in the common view, there is no problem in wearing it. As for wearing platinum, there is also no objection in wearing it.

Tawzih al-Masail (with annotation by Imam Khomeini), vol.1, pg. 140, issue No.255, Ayatollah Makarem Shirazi: "What is called white gold is treated in the same way as red or yellow gold, as an obligatory precaution, if it is called "gold".