It isn't appropriate at all op. It's not just the colour.
It is too long, too strappy, too booby for a wedding guest. It just isn't what you would wear, and would "impress" for all the wrong reasons.
VB wore a strappy, silky, petticoat-y thing to an evening thing for Brooklyn's wedding and there was a lot of chatter - and that was evening. It needed at least a little jacket (and who knows, maybe she had one for the ceremony, I'm not sure). But turning up like that in the middle of the day is just OTT.