Green is associated with Saint Patrick's Day because it is the color of spring, Ireland, and the shamrock. Leprechauns are also associated with this holiday, although I'm not sure why. Leprechauns of legend are actually mean little creatures, with the exception of the Lucky Charms guy. They were probably added later on because capitalists needed something cute to put on greeting cards.
What's good luck on Saint Patrick's
Finding a four-leaf clover (that's double the good luck it usually is)
Wearing green. (School children have started a little tradition of their own; they pinch classmates who don't wear green on this holiday).
Kissing the Blarney Stone.
Irish fairy. The name leprechaun is derived from the old Irish word luchorpan which means "little body." Looks like a small, old man (about 2 feet tall), often dressed like a shoemaker, with a cocked hat and a leather apron. According to legend, leprechauns are aloof and unfriendly, live alone, and pass the time making shoes; they also possess a hidden pot of gold. Treasure hunters can often track down a leprechaun by the sound of his shoemaker's hammer. If caught, he can be forced (with the threat of bodily violence) to reveal the whereabouts of his treasure, but the captor must keep their eyes on him every second. If the captor's eyes leave the leprechaun (and he often tricks them into looking away), he vanishes and all hopes of finding the treasure are lost.
The Blarney Stone is a stone set in the wall of the Blarney Castle tower in the Irish village of Blarney. Kissing the stone is supposed to bring the kisser the gift of persuasive eloquence (blarney). The castle was built in 1446 by Cormac Laidhiv McCarthy (Lord of Muskerry); its walls are 18 feet thick (necessary to thwart attacks by Cromwellians and William III's troops). Thousands of tourists a year still visit the castle.
The origins of the Blarney Stone's magical properties aren't clear, but one legend says that an old woman cast a spell on the stone to reward a king who had saved her from drowning. Kissing the stone while under the spell gave the king the ability to speak sweetly and convincingly.
It's tough to reach the stone, it's between the main castle wall and the parapet. Kissers have to lie on their back and bend backward (and downward), holding iron bars for support. Can you imagine kissing something that has had people's lips all over it for 500 years? Yuck!