Wearing a shamrock, or any green, was considered an insignia of the rebellion, and you were hanged for high treason. The British so feared the ethnic identity of the Irish that they would murder citizens under their rule for wearing the ethnic color.
This was in a time of the crushing tyranny of the English Penal Laws, various statues passed over centuries to discriminate against Roman Catholics and try to force the population into the Church of England. One of the earliest was the 14th century Statutes of Kilkenny that criminalized speaking Irish and banned intermarriage between the Irish and the English.
Under the Penal Laws:
The Catholic Church was forbidden to keep church registers.
The Irish Catholic was forbidden the exercise of his religion and were compelled by law to attend Protestant worship.
The Irish were forbidden to receive education.
An Irishman was forbidden to enter a profession, forbidden to hold public office, forbidden to engage in trade or commerce.
Th Irish were forbidden to own a horse of greater value than five pounds.
An Irish gentleman was forbidden to buy land from a Protestant and forbidden to inherit anything from a Protestant.
The Irish could not be a guardian to a child, could not, when dying, leave infant children under Catholic guardianship, plus could not personally educate a child or send a child to a Catholic teacher, and could not send his child abroad to receive education.
And to wear green was a capital offense of high treason during the 1789 rebellion. So, when I see people who paint their faces green for the parade, or when Chicago dyes its river green or New York its beer, or some hipster in Portland dyes their dog green; it honors, in a subtle way, those murdered for trying to keep their ethnic identity so deeply associated with a color.
In celebration of the perseverance of the Irish people, here are a few magazine covers of our favorite Irish Gentleman: