It's sorted based on something and then the lesser users are greyed. I think after 5 posts you become less greyed and then after 10 posts you get full color. It's so people who nobody knows don't show up in the middle of the list. You can easily look and see what active members are on. Back when people used to play the arcade, it was annoying to see all of them and have to look through the 15 listed users to see the 4 active members that were online.