Good clarification, Cake, thanks :)
The NCT factsheet is for babies up to about a week. After that age, you're on your own!
Green poo is a very frequent worry on the mumsnet boards - at least once a week, often more.
In a baby who is thriving, it is not significant. It can mean the baby is fighting an infection ( but is not actually ill with the infection).
All it is, is a reflection of the speed of transit through the gut. Poo turns yellow when it's been in the lower bowel a little while - if it comes through a bit faster, it's not had time to turn yellow and it is green or greenish.
If the milk the baby has had is lower in fat content, it goes through the gut faster ('cos fat slows down the transit time). This doesn't matter - the baby gets what he needs from the milk just fine, unless there is something else going on (metabolic disorder, baby not feeding effectively) but in these situations the baby is not well and you get other signs and symptoms of this.
Most babies who poo green are normal, healthy babies, getting the 'full fat' they need and thriving.
Probably all babies have the occasional green poo, and some babies always poo green.