As babies hedgehogs are very inquisitive about their surroundings and use their sense of taste and smell to navigate through their surroundings. This means licking and tasting almost anything they come into contact with. This also means that they are sending all sorts of new and different bacteria through their systems. This can make their poop green colored or even slimy at times.
This is extremely common and normally will be worked out naturally as the baby gets a few weeks older. In rare instances this can fester and become a bacterial infection that required antibiotics from a vet. Adults rarely get this but it can happen from time to time. If the baby only has green poop and no other concerning symptoms then I only monitor and make sure baby continues to eat and drink. If there are any other concerning symptoms such as not eating or drinking normally, losing weight or behaving lethargic then a vet visit will be in order.
In conclusion green poop is ok- to an extent. Use your best judgement and its never a bad idea to take them to the vet to get checked out if you are concerned.