A Ninja makes a wonderful looking tattoo. These Japanese warriors look pretty bad ass on anyone.
In my opinion, they look really nice in black and grey, but color is nice as well. Some people get just a Ninja weapon or a symbol. It is all up to you. Just be creative and you will be satisfied.
Many people love the Christmas season so much that they get tattoos inspired by the holiday. I have seen everything from Santa, snow, The Grinch and more. Men and woman have gotten these awesome tattoos. Just try and be original. Get a good artist to do it.