Complex sentence: In choir dress that is when he wears a cassock, rochet and mozzetta, the pectoral cross is usually suspended by a cord of silk; green and gold for an archbishop or a bishop and red and gold for a cardinal.
Split into simpler sentences: In choir dress--that is, when he wears a cassock, rochet and mozzetta--the pectoral cross is usually suspended by a cord of silk. This cord is green and gold for an archbishop or a bishop, and red and gold for a cardinal.