What is the meaning of the clothes the bishop wears at Confirmation?

The "special" clothes (called liturgical vestments) worn at Confirmation were originally "ordinary" clothes. The white garment (alb) that priests and bishops wear under their other vestments was the garment that ordinary Romans in the first and second century wore around the house during the day.

When they went out in public, they put on a tent-like colored garment (chasuble) over the alb just as you might put on a jacket over your shirt when going out.

The tall, pointed hat (miter) the bishop wears was originally just a hat. Little by little (in the 13th and 14th centuries), it became a sign that the one wearing it was a "high priest." In early days, priests and bishops got a special haircut (tonsure) and a round spot was shaved off on the top of their heads.

The little round hat (zucchetto) kept their shaved head warm in the winter Eventually, it too became a religious sign. The pope wears a white one; the cardinals, red; bishops, violet. When other priests wear one, it is black.