There are many different user groups in the forum, which for the most part correspond to your position in HOL. In the board statistics (the active users list at the bottom of the forum main page) usernames appear in different colors. Each color corresponds to a user group.
For example, Novices are grey as well as Guest Students and Guest Professors (old HOL members), First Years are blue, Second Years are green, Third Years are pink, Fourth Years are cyan, Professors/Staff are orange, Prefects are purple, Head Students are dark blue, and Admins, Headmaster, Head Office members, and Head of Houses are all red.
Novices is the user group for people who are not part of HOL (yet). It is the default User Group. You'll stay in this group at first, even if you're a HOL Student already, as your forum account will need to be updated by an Administrator and this can take some time, so please be patient. Admins are in charge of the forum and take care of the problems linked to it - For forum questions and problems, PM them, and only them.