I like a white-blue-brown-black sequence. Blue denotes someone who is capable of falling safely. Brown can be given to someone who has 'assistant instructor' status.
Even those these colors in some sense correspond to kyu ranks, they wouldn't have to. You could have everyone wearing white, plus a shoulder aptch or something.
In my present dojo, you can tell the real newbies because theya re in street cloths. We don't recommend that they get gis until after a month or so. They usually get a hakama after about six months in the dojo. Even though we give people colored belts, you can't see them!