You can see pictures from the event this year by clicking here. Note that there are a total of three pages of photos (scroll at the bottom of the first page).
Anyway, the reason that they are all three wearing black is that on the day of the prom promise re-enactment a number of students wear solid black to represent the students that are killed each year in prom related crashes. These three happened to be a part of it this year. This photo was taken after school (I usually pick them up).