No mystery about it. The fur comes in contact with the placenta fluid that is green. Usually if it happen, it happens to the last pup born.
Weird thing about my pup is that she was born on St Patrick's Day
You answered it.
Maybe I'm just greenaphobic.
Used to be involved with breeding West Highland White Terriers. It’s more obvious on white coats, but green staining from the birth process is quite common. We frequently had 1 or more “green” puppies.
I used a different shampoo on one of my JRT’s it turned him pink. Not cool for a tough male JRT.