Someone posted in the original Ehell forum back in Delphi that it was okay to wear black to an evening wedding in NYC, but not to a daytime wedding in Atlanta.
I know there are a lot of gray areas in between- those are the two extremes.
But I am very glad nobody wore black to my morning wedding in the South.
Why would it have made a difference?
Daytime black could look pretty funereal. Because funerals are in the daytime, so anything slightly dressy in black would be the thing you chose to wear to a funeral.
Eveningwear black would not look funeral--the fabric would be very different, as would the cut.
Time was that people always wore black to funerals. And they wore black for weeks or months if there was a death in the family. (also, black clothes weren't normally considered fancy, because it was hard to keep them a deep black, because the dye would fade; it's an extreme color, dye-listically speaking)
It's not quite as prevalent as it used to be; more people just wear nice clothes that aren't particularly bright. But it used to be a big deal.