The color green neutralizes red. Since the two colors are opposite from each other on the color wheel they are considered complimentary to each other. As with all complimentary colors, if they are mixed in the proper proportions a neutral color will be produced (grey, white, or black). This concept is often used in cosmetics and the film & television industry! Wearing a green shirt is like a visual illusion and helps to reduce the appearance of red, especially on your face.
Have a great St. Patrick's Day, and as always, drink responsibly!