White goes with everything, especially on Easter Sunday in Rome. However, wearing white is not a fashion statement and it’s not the reason a pope wears white.
Small ‘t’ tradition holds that it was was Pope Pius V who started the tradition of the white Cassock. He belonged to the religious order called the Dominicans, or the Order of Preachers, who were also called the Black Friars because of the black cloak or cappa which covered their white Habits.
Antonio Ghislieri, elected to the Petrine office on January 7 1566 as Pius V, wished to continue wearing the white cassock of his Dominican confreres. Some sources contest this story on evidence that portraits painted before the time of Pius V show popes wearing a white cassock [see additional notes below].
What is certain is that white is the colour that symbolizes holiness and purity throughout sacred scripture and in capital ‘T’ Tradition (the living teachings or Magisterium of the Church from it’s institution by Jesus to the present day) and it is a record of history that St. Pope Pius V, as his very name indicates, lived a holy and pure life [see additional notes below].
“His interior state reflected the whiteness of his exterior garments, you might say”, and it has been noted that the reason why popes since Pius V continued to wear white is “a tribute to the sanctity of the Dominican pontiff, who refused to shed his community’s habit on his election to the papacy”  that we may understand as a sign of humility and piety.
Next time you wear white on April 30th, Pius V’s official feast day, remember “his holiness,” say a prayer and consider what you might do on that day to grow in inner whiteness.