It's a part of their shinobi code.
They sneak their way through any situation without anyone noticing them..Of course, every great ninja needs some accessories! You can wear a ninja outfit that draws all the attention to you, instead of something that will keep you hidden away. It has a wet-look finish that might not be great for hiding in the shadows, but it's amazing for flashy ninja-style moves! But when you're really trying to kill it at the next costume party.