We have always done black..and honestly I have to say I am not sure why either. Perhaps it is to signify how important the ceremony is and to show respect, thats what I have always taken it as. I see black as a very formal serious color, so I like to think of wearing black at pref as respect. We usually go with lighter decorations and everyone has a variation on how they dress in black. One girl had just gotten a pair of candy red Stuart Weizman pumps and decided to sport those at my last pref...it definately jazzed up the place
Since we don't have a house on the campus I came from we would have to walk to a private lounge on campus in order to perform ritual and initiation. We would always get looks as 30 girls came across campus dressed in white. So in that respect, I like the black a lot better
I love pref...I am hoping to go back this year as an alumni to help out.