On the box test, you forgot the fourth category: Thaumiel- i.e. the anomalous object is the box.
Also if you take a look into some of the earlier SCPs, you'll find that originally the categories corresponded to to threat level, which has regained traction in a new form designated by colors, though these have not yet been universally applied. http://scp-int.wikidot.com/niveaux-de-menace-des-objets-scp