Crosses making me cross

I've tried posting this question on another forum many times now but someone always posts after me and my questions isn't noticed, so sorry for the new forum on the same topic. I'm still missing one Saint Cross. The only places in the hall of doors I haven't managed to access are the back door in the hall of confusion (assuming it's nothing), and whatever the three colored globes do when you hit them. Haven't found anything in the game referring to three colors in a row, and I've progressed to the jailhouse at this point.