Office of Grand Ayatollah Khamenei (may Allah grant him long life):
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.
Office of Grand Ayatollah Sistani (may Allah grant him long life):
It is haraam for men to wear gold (even though its color may have become white due to plating), like hanging a golden chain on one's chest, or wearing a gold ring, or to use a wrist watch or spectacles made of gold, and the prayers offered by a man wearing these things will be void. As for wearing platinum, there is also no objection in wearing it.
Office of Grand Ayatollah Makarem Shirazi (may Allah grant him long life):
Wearing gold ornaments is not allowed for men regardless of its color (even if it is white) and the prayer offered with gold is void. However, there is no problem in wearing platinum which a different metal.
Office of Grand Ayatollah Saafi Gulpaigani (may Allah grant him long life):
If it is really gold and only its color is white, it is not permissible to wear it but if it is platinum, which is a different metal, and only its name is gold, there is no problem in wearing it.
The answer given to the above question by Ayatollah Hadavi Tehrani (may Allah grant him long life) is as under:
It is haram for men to use any kind of gold ornaments irrespective of whether they are in the form of a gold ring or a necklace or a gold-plated watch wrist. If white gold is the same conventional white gold which has the same value of the yellow gold, it is in reality the white gold which has been blended with white metal to get that white hue. It is therefore haram for men to wear it. However, if white gold refers to platinum which is dearer than gold, it is permissible for men to wear it.
Link to Esteftaat Website (code 1206)