A “zucchetto” is a small round skullcap worn by Roman Catholic ecclesiastics in colours that vary according to the rank of the wearer. Amaranth is the colour of purple amaranth flowers. This is the colour of the “zucchetto” worn by Roman Catholic archbishops and bishops. The pope's “zucchetto” is white; those worn by cardinals are scarlet while priests and deacons wear black “zucchettos” (or “zucchetti”). The caps are very similar in appearance to the Jewish “kippah” or “yarmulke”.

The “zucchetto” comes in the shape of a hemispherical skullcap with a twisted silk cord stem, known as a “stirpis” or “stirpes”, sticking out from the centre of the cap at its crown. This cord distinguishes between the “zucchetto” and the Jewish “kippah”.

There are certain protocols to be followed in the wearing of the “zucchetto”. Lower ranking ecclesiastics must remove their caps to those of higher rank while all “zucchetti” must be removed in the presence of the pope, unless excused from doing so by the pope. The “zucchetto” is worn and removed at different phases of the Mass and usually there is a “zucchetto” stand known as a “funghellino” ("little mushroom”), near the altar, to place the “zucchetto” when it is not being worn.

More Info: en.wikipedia.org