As far as wearing white dresses... No special color of dress attire is required for ceremonies for us. But while I can't speak with regards to ritual and a specific color - I do know from experience that white and lighter color clothing turn out so much nicer for photographs. Our charter memebers photograph was "proffesionally" taken a few hours before the ceremony. Most of us picked out dark blues or blacks for our dresses. Between the background, each other's dresses, and those of us with brown/black hair - the photo could have been a lot nicer had we all worn lighter colors...

just my few cents to the pot.. (this could actually be an interesting fund raiser..)