So, you will be relieved to know that I am not going to add my two penn'orth to the cause but I am going to feature some extracts from posts on the subject (prompted by an innocently meant comment I left on A Reluctant Sinner's post about the new Bishop of Wrexham Diocese) - you may see the post here - http://areluctantsinner.blogspot.co.uk/2012/06/new-bishop-of-wrexham-is-priest-of-same.html
So, first off, a H/T to the Father Joe blog for this:
What do you call the black pants and black clerical shirt a priest wears (with a white collar tab)? They are simply called clerics or clerical clothing. The shirts actually can come in various colors and sometimes Norbertines, Dominicans and others might wear a white clerical shirt. Bishops in some of the hotter climates have permitted this to ease the problem of heat absorption by black clothing.
PRIESTS ARE SUPPOSED TO WEAR CLERICAL CLOTHING. If the priests you know are not doing so, then there is a serious question of disobedience. Church law insists that the priest wear “suitable clerical clothing, according to the norms issued by the Episcopal Conference and according to legitimate local customs.” (Canon 284)
And, from Aggie Catholics we have this:
The black represents a priest dying to self as well as simplicity/poverty. Every time he puts on his clerics, he should remember that he does not belong to himself, but his bride, the Church. It also symbolizes simplicity and giving up the comforts, honors, and privileges of the world.The white Roman collar you see priests wearing symbolizes obedience to God and the Church. This comes from the tradition of a slave having a ring put around their necks and priests choose to give their lives to Christ as his "slaves". It also represents the marriage "ring" of being we to the Church. The white also symbolizes the resurrection of Christ.
And, finally, a very fine post from Fr Andrzej Pryzybylsky
The day when I received a priestly dress was a unique event for me. Although I did not become a priest then (actually we received cassocks at our III year of studies in the seminary), we belonged to clergy in the eyes of the world and people. It was a marvellous day! Some people began greeting Christ when they saw me, and they began sharing their problems. Thanks to the cassock I became a visible sign of a special belonging to God. Therefore, I support the defenders of clerical clothing and although I know that it is not true that 'clothes make the man' I miss the times when wearing a cassock was a normal and daily habit. I like wearing my cassock very much.
Naturally, in the first centuries of Christianity (for over four centuries) priests wore the same clothes as ordinary people. The tunics were normal clothes. When it was fashionable to wear shorter robes some priests kept tunics, and thus they stood out from other people. The Synod of Braga, AD 572, ordered priests to wear different clothes when they went out. The tradition of wearing cassocks was established over a very long period. At the turn of the 15th and the 16th centuries there was a custom of wearing robes called 'révérend' (the word derives from Romance languages). In those times men used to wear robes, especially the gentry liked wearing long dresses: the zupan (a long coat lined with cloth of gold) and the kontusz (an overcoat with split sleeves) and belts. The clerical clothing was established in the 17th and the 18th centuries. The colour of the cassock was connected with the hierarchy of clergy, which has remained up till now: the pope wears a white cassock, cardinals wear red (scarlet) ones, bishops wear amaranth red ones and priests wear black ones. You are right that black is associated with sorrow but in the case of priestly robe this colour has another symbolic meaning. A black cassock is to remind a priest that he 'dies to the world' every day and immerses in eternity. Blackness also symbolizes giving up bright colours and thus giving up what the world brings, its glittering, honours and entertainment.
The clerical collar is an important item of clerical clothing. Our students used to ask me: why is this white belt on you neck called a clerical collar although it is not colourful (in Polish 'koloratka' means colourful)? The word derives from Latin collare meaning a collar (also called a dog collar). A white collar on a priest's neck should remind him of a ring and collar - his marriage to Christ and to the Church and giving his freedom to Christ, thus letting him control his life. We, priests, wear a collar because we want to be directed by Christ in all things. Please notice that our collars are white as opposed to our cassocks. In the background of a black robe it is a symbol of the light of resurrection. We go through the world giving up baubles and colours, living the hope of participation in the brightness of resurrection. This white collar in the background of our black dress is actually a sign of our desires and aspirations.
See how meaningful our robes are and therefore I am sad to see that priests wear cassocks less and less frequently since a cassock itself has proclaimed the most important truths of our faith. And by the way, we, priests, wear trousers under the cassock and it is not a rule that every cassock has 33 buttons.
So there it is. A black and white answer or answers, nothing grey about that whatsoever.