Gremlins, imps and quasits too, it seems.
No idea why are they actually represented by "I", other than the fact that "&" ran out of colors.
They belong to a group of minor demons after all, save maybe for gremlins.
Imps and quasits could be white or light blue "&".
Although the latter is already used for djinnis, those are arguably the rarest monsters seen walking around, they can literally only show up when a player uses a non-blessed RoDS, which doesn't happen too often.
Anyway, I think any single change right now would have a high chance of propagating and forcing more changes somewhere else and that's something I wouldn't want to see as a player.
I got used to stuff looking one way so it's ok to add new stuff, but not so ok to change existing things.