It just looks like something that was made for a bridal party. I wouldn't feel happy wearing it on the off chance even if it is grey, in sunlight it will look white.
To an extent it depends what you wear with it, if you're wearing a coloured top underneath, brightly coloured accessories etc then maybe but as per the photo with shirt/waistcoat then no- I wouldn't. You can always ask the bride?
No plans to marry as it's just not for me but if I did I think I'd make a point of saying in the invites to wear whatever you bloody like/go all out/get your old wedding dresses out if you fancy and get a wear out of them- it would be great fun!