Back in the dark ages, we did a sort of sky blue for pref.
Each girl chose a dress pattern to suit herself, and all the dresses were made up in the same material, which was ordered in bulk. You could have your dress made, or have your mom make it, and some of us made our own.
One of the chapters I advise switched to purple dresses for preference this year. (Dark, deep jewel-type purples, not lavendar or lilac purples.) It looked great! And, purple was a huge color last year, so it was pretty easy to find! I think they are going to stick with it.