Green has nothing to do with St. Patrick. He often wore blue, a color that was tied to Ireland during Henry VIII’s reign. In the 1800s, the Irish started an independence movement to divide from the British and chose green as a symbol of their country. Drinking green beer and pinching each other is an Americanized way of honoring a saint who wore blue- so basically, if St. Paddy were still around, he’d be pinched by Americans on his own holiday. Source, Source 2, Source 3