My 22yr old daughter has colored tattoos. What kind of ink was used to make tattoos years ago?

My 84yr old father got tattoos when he signed up to join the army, for WWII. His tattoos now look like it is greenish in appearance, not black ink. So, I'd like to know if someone can give me an answer!
Even when I was a child, his tattoos always looked green! Is it the ink? Or is it because where it was done?

is it true that tattoo lettering will bleed to become illegible after about 10 years?

i am wanting to get a small passage from the bible or a section from a religious song no more than 60 words tattooed on my side over my ribs. the entire tattoo would barely fit on a standard sheet of paper. The verse would form a cross with no outlines. I would most likely use thin cursive lettering. However i want to make sure it would last. help please?