Personalized Happy St. Patrick's Day Shamrock Silhouette in White T-Shirt. Get in touch with your Irish luck in our festive Happy St. Patrick's Day Shamrock Silhouette T-Shirt - Retro Heather Black. Makes a fun St. Patrick's Day gift for brother or sister! Everyone loves our Custom T-Shirts! Wardrobe essential for looking good, 24/7. 5.0 oz., pre-shrunk 100% cotton. Seamless 1x1 rib collar. Shoulder-to-shoulder taping. Double-needle stitched sleeves, bottom hem and front neck. Note: greys are a cotton/polyester blend.