Happy St. Patrick' s day to everyone!
It's not a holiday in Italy but due to globalization and the fact people here travel often to English speaking countries to learn English we know how much is important for Irish people in Ireland and abroad.
A little curiosity that comes from Wikipedia: St. Patrick used the shamrock, a three-leaved plant, to explain the Holy Trinity to the pre-Christian Irish. The wearing of and display of shamrocks and shamrock-inspired designs have become a ubiquitous feature of the saint's holiday.
To tell the truth the colour that was long associated to the Saint was blue but because of shamrocks and because green is the predominant colour of Ireland from about 1750 D.C. there was a change.