Something I did waaaaaaay back in the day, with some help from this very monastery, to support "anonymous" chat in a site was to do colors based on IP (such that the IP was not displayed, nor reversible, but used to make a hashed color for display of the user's chat session). It's only a good transitory/ephemeral solution though for something like chat and not so hot for the reasons you elaborated: temporal, IP/browser changes, etc.

For your list, JS magic will be disallowed, I expect. And you can't rely on JS for client-side enforcement anyway (with hackers at least).

For the rest: it could work quite well a lot of the time but at least some of the time it will lend a false sense of division to a single user no matter how it's done. With an IP anonymizer and two or three or four... browsers it would be pretty easy to appear to be a gang when it's really just one. And the more specific/careful the technique for keeping the AMs separate, the more likely a single anonymous monk will accidentally appear to be two or more. :|