Aside of the liturgy, clergies have various options of clothes to wear. For casual occasions, they most wear the simple black shirt with a white roman collar.
When going for more formal events, or when walking through St. Peter’s Square in Rome, bishops, cardinals and monsignors do wear a cassock that is indicative of their office.
Each of their cassocks have distinctive colors, but from afar they are not easily distinguishable. It appears more difficult to distinguish them when they wear a black cassock with only the piping and sash being a different color.
Here is a quick explanation on how to identify each color and its symbolism.
Over the centuries, the pope was accustomed to grant honorary titles to priests within his Papal Court. There were plenty degrees of honors, typically only given to priests who worked closely with the Holy Father in Rome.
The title of Monsignor was expanded over time and given to priests outside of Rome with the recommendation of a bishop, but was limited recently by Pope Francis, returning to the older practice.
As members of the Papal Court, monsignors wear the color purple. Monsignors typically, do not have a zucchetto (the skull cap) or a pectoral cross, and that distinguishes them from bishops and cardinals.
This color purple (which is similar to magenta) was connected to the tradition in the Roman empire to vest new dignitaries with a purple toga. In the medieval heraldry the color symbolized justice, regal majesty and sovereignty.
For some of Church history, green has been the color for bishops. And this color is still seen on the traditional coat of arms that every bishop chooses when being elected.
However, during the 6th century the color was switched to “amaranth red,” which is named after the color of the amaranth flower. Practically, it resembles the color fuschia more.
As it is a color similar to purple, it holds a symbolic value that points to the work of the bishop to govern his local diocese.
Aside from the color, bishops wearing their cassock can be identified by their zucchetto and the pectoral cross hanging over their chest.
Technically, the name for the color that cardinals wear is “scarlet.” This color creates a difference for them as members of the College of Cardinals and a “Prince” of the Church.
When the Pope puts the biretta (a hat with 3 or 4 stiffened corners worn as part of liturgical dress) on top of the head of the cardinal, he says , “Accept this scarlet as a sign of the dignity of the cardinalate, which signifies your readiness to act with courage, even to the shedding of your blood, for the increase of the Christian faith, for the peace and tranquility of the people of God and for the freedom and growth of Holy Roman Church.”
Interesting enough, the bird known in North America as the “cardinal” was named after this class of Roman Catholic clergy.