What you have to have to keep chromides schooling is a blue velvet damsel, otherwise known as 'devil fish'. Terror is a real convincer...
I had one. Mine schooled and got under cover well before dark...
Seriously, our tanks aren't big enough, but if you want a busy fish with high color, get a single chromis. He'll be so active you'll think there are three of him, and as only the dominant in the school is usually high color, you do get the high color.