There is nothing wrong with a woman wearing a white wedding dress
There is nothing wrong with a woman wearing a white wedding dress on condition that she does not appear in it in front of men who are not her mahrams, because usually wedding dresses are adorned and decorated, and we have already stated in the answer to question no. 39570 that one of the conditions of women’s hijab is that it should not be an adornment in and of itself.
With regard to it being the dress of kaafir women, that is not the case. Rather many Muslim women nowadays, if not most of them, wear this kind of dress.
Shaykh Ibn ‘Uthaymeen was asked:
What is the ruling on a woman wearing white for her wedding as it is known that this is an imitation of the kuffaar?
It is permissible for a woman to wear white so long as it is not in the same form as men’s clothing. With regard to it being an imitation of the kuffaar, that is no longer the case, because now all Muslim women wear such clothes when they are getting married. The ruling depends on whether the reason for it is present or not. If it is no longer an imitation of the kuffaar and this has now become something that is common to both Muslims and kaafirs, then the ruling no longer applies, unless something is haraam in and of itself and not because it is an imitation of others. Such things are haraam in all cases.
Majmoo’at As’ilat tahumm al-Mar’ah, p. 92.