Originally, blue was the colour associated with Saint Patrick's Day.
There is even a particular shade of blue associated with Saint Patrick known as Saint Patrick's blue.
Green has long been associated with Ireland because of its verdant landscape.
There was also a tradition in Ireland of wearing a shamrock on St Patrick's Day as a symbol of the Holy Trinity.
During the Wexford Uprisings against the British in 1789, the wearing of the green became a symbol of Irish rebellion. Green uniforms were worn by the rebels.
In the United States, wearing green on March 17 has been a means of identifying with an Irish heritage.
The first St Patrick's Day parade in Boston was held in 1737.
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