A reader writes, "My questions concern clerical garb, specifically clerical shirts.
What is the significance of the tab collar? Where does it come from? And why do bishops wear purple?"
Clerical collars are detachable white pieces of cloth or plastic that are attached to specially-designed shirts with two metal studs. There are two major types: The "Tab" Collar, which is pictured above and is generally favored by Roman Catholic and Eastern Orthodox Priests in America, although some Protestants wear them.
This is the round, or "Dog Collar." (And yes, that is Tim Curry, who in addition to Frankenfurter plays the priest in the opening scenes of The Rocky Horror Picture Show.) This collar is favored by most Anglicans, Lutherans and some Methodist ministers. Also pictured here are "Preaching Tabs" (which are fairly uncommon these days) that designated which clergy person was preaching that day.
But where did it come from? The origins are hazy. As is true with most clergy garb, at one point, such collars were common wear among all men, although they usually attached at the front, not the back. Many clothing historians simply theorize that such things are holdovers by the more conservative clergy while other fashions changed.
We know that the Roman Collar dates from around the 17th century, but the "Dog Collar" did not become popular until the late 1800s. (The detachable collar was invented in 1827.)
There is a lot of theorizing about what it symbolizes. Many will talk about it as the "yoke" of the Gospel. This is probably an added-on meaning.
I think in many ways it is simply a uniform. Much as a firefighter or policeman is accorded certain status and function due simply to the uniform, so it is with the "clerical uniform."
There has been a lot of debate in the last few years questioning whether the uniform is good or bad. While it does confer status, not all of that is positive. And while it can get you into certain places such as hospitals, etc., it can also exclude you. I generally assess each ministry opportunity as to what dress would be appropriate and whether the collar would help or hurt. When I'm on campus on Wednesdays, I wear the collar. When we are doing our Friday night relaxed stuff, I wear church-related "Civvies."
There is a semi-serious tradition I heard about in seminary - that you can tell the churchmanship of an Anglican priest by the height of his/her collar. The higher the collar, the lower the churchmanship.
The purple coloration for the shirts and cassocks of Bishops (Like Desmond Tutu here) is likewise something whose origins are shrouded in mystery. Some claim that it is because it is the color of penitence and that bishops are supposed to be reminders of that. Most costume historians believe it is because in the Roman Empire, purple was the color reserved for royalty as purple dye was very expensive. Since bishops have sometimes been called "Princes of the Church," this is quite likely another example of conservation of fashion.
Another anecdote I have heard is that you can tell which missionary society an African Anglican bishop's diocese was evangelized by due to the coloration of the purple. Dioceses evangelized by the high-church society wear a more magenta purple like Tutu. Dioceses evangelized by the Evangelical society wear a deeper purple. I'm not sure about the veracity of that.