No idea. I have a vague understanding that colored coins are a work in progress and may be added at some point in 2013

I have been looking into the protocol for how this works. It doesn't require anything additional to be added (to the bitcoin daemon). To be practical it does require that clients are made that process them conveniently, this is what is the work in progress and does seem to be at the 'usable in a stable form some time this year' point.

The above distinction matters to me because it influence whether it is something I can just use if I find customers who want it and I am willing to do some coding to facilitate it versus features that require creation of a Bitcoin Improvement Proposal then the politically influence of a miners to start adopting it. For example zerocoin (the solution to anonymity and privacy) would require huge political advocacy to get into play in the existing bitcoin currency.

but I've never seen anyone lay out a list of the scripting language elements with the enabled and disabled ones specified.

Indeed, my research has failed to turn up such a document too. The information that is out there is also significantly out of date unless pieced together rather carefully. A summary of the availability of the features that are of interest. I am reasonably confident in these findings but not certain. (90% confidence.)

• Timelocked transactions: The protocol (and actually in use bitchain) supports it but miners will nearly always reject transactions with future dates. This seems stupid to me but there doesn't seem to be any strong pressure to start accepting them. It is still possible to create such transactions and store them until the time is up then send them in. This solves some timelock usecases but the possibility of double spending prevents it solving many other use cases.
• Multisignature transactions. ie. Escrow. Transactions that require n of m signatures in order to spend the output. These work. Technically. You can create them manually via the command line, send them to the blockchain and then use the command line and use of or access to someone who will cooperate with n of m signatures to create transactions that spend them. But current clients don't do this for you (except in the crippled case whereby if you have m of m keys in your wallet it will deign to let you spend them.) But this feature is there to be used if you want it.
• Zero Knowledge Proofs eg. Zerocoins. Reliable privacy and anonymity right there within bitcoin. The research and cryptographic technology is available. As are proof of concept reference implementations. But this system (or an equivalent or superior one) isn't accepted and likely will not be for at least several years. An alternate currency could do it today.

Since this is such an obscure area of Bitcoin, you probably will have to read the source to find out.

Done. Now I'll have to read the source even more to work out how to make clients that use the (available) features to serve my purposes.