With St. Patrick's Day approaching, I've got green on the brain. While the hue is omnipresent in every garden or vase, it's a curious occasion when a flower's petals match its foliage. If a four-leaf clover is a sign of good luck, an equally rare green flower must be a friendly force, too. Come along and take a lesson on flowering plants of shades of lime, chartreuse, and every green in between.