I received a question via e-mail:
Recently we have been trying to introduce the Tridentine Mass to my parish, and fortunately we now have a new priest who is open to tradition. We have yet to overcome several obstacles, including sending our priest to be properly trained, but I am confident our efforts will be realized. I have offered to serve Mass in the Tridentine form and I have ordered the necessary literature and training information. My problem is I have looked online and have had no success in finding instructions on what garb I am to wear. I assume a cassock and surplice, but I was wondering if you could inform me of any rules regarding dress and also a quality site to order from online. These questions may seem very obvious, but my parish is currently very uninformed about most aspects pertaining to the Tridentine form. On a separate note: I am an avid reader of your blog and I truly enjoy your posts.
Thank you for your time.
In a pinch, anything decent would serve, so to speak. If necessity strikes, wear your "Sunday Best".
However, the traditional garb would be, as you surmise, cassock of some color, black might be best depending on what the priest wants for his servers, and white unadorned surplice of some style.