According to the verdicts of grand religious authorities, it is not permissible for men to adorn themselves with whatever is called gold irrespective of whether the gold is yellow or red or white. However, it is necessary to note that platinum is not gold; it is a different metal.
Therefore, if it is known through checking a metal with an expert that it is white gold, it haram (forbidden) for men to wear it. As for wearing silver, there is no problem in wearing it.
 - 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".