Yep, Vitamin B can do it. A few vitamins will do this. Eating asparagus will definitely turn it much greener and also it smells. I knew about the jaundice, Esther, I was trying to avoid mentioning it - it happened to me, too (perils of living in student digs - one step away from being on the streets, although I think living on the streets would have been healthier). I got jaundice as a complication of glandular fever. I've also had different liver problems since - it doesn't always show up in the urine. But yes, it can look like a cup of black tea. If it's liver, a dip stick test for bilirubin will be positive - quick and easy. And if it IS positive - the liver is an amazing organ, it can regenerate better than any other organ providing you KNOW it needs some help. Some medications can stress the liver too - you do need to know.
There are other possibilities too, all need checking out.
I remember once a huge panic - my kids' nappy contents were a ghastly beet red colour. I was in full panic, until I found a blob of home-made play-doh in their clothing. Turns out that the intern at the child care centre had put too much colouring in the play-doh, turned it dark purple. And kids eat play-doh, don't they? The colour went right through them, it really looked spectacular. I was very glad to not be using cloth nappies at the time - they would have been permanently stained and I wouldn't have liked to have to explain THAT when I dried the nappies on the line! But I do know some of the other parents did take their kids to the doctor, who was puzzled and concerned, but the kids checked out OK. The doctor wasn't upset at the false alarm - he was relieved it was nothing serious. And he's probably still dining out on that one!