Allison over at YIM Catholic shares this question and the answers (both student guesses and the answer the parish catechetical leader offered). Great post!
First, the answers that the students and parents give:
One parent suggested priests were in mourning over Christ's death. A child said maybe priests wore black clothes because don't show dirt as easily. Another thought priests were depressed. Obviously, we were all stumped.
The parish catechetical leader's answer?
The black represents penance for humanity's sinful condition and that little white square the hope of salvation. I had never considered clerical garb in this way. I found her explanation comforting: we're all sinners on journeys, traveling with hope to our destinies.
I did a little research on clerical collars and discovered for most of the Church's history, priests did not wear special collars of any sort. At the end of the 16th Century, priests started wearing white collars, following the fashion of the day. The collar didn't start out having any special spiritual meaning. Today that collar is a signal to all that a priest is ready to administer sacraments - including Anointing of the Sick - at all times. By wearing these collars, Catholic priests offer visible symbols to the world that Christ is among us.
The Directory for the Ministry and Life of Priests, prepared by the
Congregation for the Clergy and approved by Pope John Paul II on January 31, 1994, lists 23 reasons why priests should wear Roman collars.
Reason #23 includes a point all of us - lay, consecrated and religious - should take to heart.
"Your life is not your own; you belong to God in a special way,
you are sent out to serve him with your life. When we wake each
morning, we should turn our thoughts to our loving God, and ask for
the grace to serve him well that day. "