Colzani was born near Bologna and made his debut there at the Teatro Comunale in 1947 in Lohengrin. He first sang at La Scala in 1952 as Alfio in Cavalleria rusticana.
He debuted at the Metropolitan Opera debut in 1960, when he was asked to substitute for Leonard Warren in the title role of Simon Boccanegra. He remained with the company for 16 seasons, singing more than 200 performances.
Colzani's last performance at the Met was in Adriana Lecouvreur in February 1978, singing alongside Jos_ Carreras. Colzani sang alongside opera stars including Maria Callas and Renata Tebaldi; at La Scala, he sang with Franco Corelli.
His repertory included Riccardo in I puritani, Nabucco, Don Carlo, Falstaff, and Carlo G_rard in Andrea Ch_nier.
He died in a nursing home in Milan after a long illness, according to the AP. He is survived by his wife, Ada, and two daughters.