This is tricky, isn't it? I hope someone with more experience comes along and has a better answer for you.
In the meantime, I will tell you that I was surprised (I think I've mentioned this before) at the last evening wedding reception I went to most women wore something with black in it. I don't know if black is just a popular clothing color now or if everyone just prefers it. Most were in dresses. I wore a pantsuit because I don't like dresses. And I wore blue. I am a friend of the groom's mother and I simply asked what color the wedding colors were. I showed up at a wedding once wearing the same colors as the wedding party. Awkward!
Maybe that's why so much black. Maybe nobody wanted to match the wedding party. You have to be careful of that now, though, because a lot of weddings are black, white, red (or some other color) themed.
Here is what I know for sure. Nobody and I mean nobody cared about what I wore. It was all about the bride and groom and that they were having fun. I wouldn't have shown up in jeans and a t-shirt, but you know what I'm saying.