The three-color system is so pervasive, that now I notice exceptions. So far there's only one: Ousai Academy of S.Y.D.. Pictured: Mitsuba, who is a year off the other members, if I understand it right. I may be wrong about her in particular, but there aren't any diffierent colors at any kind of group event either.

They may still have color-coded student IDs or other tokens. But I'm not going to rewatch the whole thing to make sure.