Green stools are not uncommon in hedgehogs. It can be caused by a variety of reasons, including stress or illness. Green sticky or slimey moucousy stools can mean an irritated gastrointestinal system but it can also indicate an infection. If it is a dark green sticky or slimey mucous which happens more than once especially if accompanied by loss of appetite and decreased activity, a vet visit is needed asap.
Stressed induced green stools can be caused by something as simple as a new home or a new food was introduced. At Hornbeam Wood Hedgehog Sanctuary we have noticed this happen on occasion when rescued hedgehog arrives and is put in to a new home, but mostly when their diet is changed. When this has happened they settle down within a day and the stools return back to normal. However, if there is any concern that a hedgehog is sick, you should take him to a veterinarian as soon as possible.
If the stool is sticky it might also contain some mucus. Mucus indicates a gastric upset which can happen if the hedgehog has changed food types, often in this case a hedgehog's stool will start to return to normal within a day or two.
It must be noted though, even if there was a new food introduced, if the hedgehog is losing weight, not eating, not drinking or their stool continues to get worse, or blood should appear a veterinary visit is required ASAP.
If nothing has changed, and the green, mucousy stool, cannot be explain, the hedgehog will need to see a veterinarian. As long there is nothing else abnormal, it might be worth waitiung a day ot two to see if the stool starts to return back to normal. But any change that indicates it is getting worse would need a visit to a veterinarian.
If the hedgehog is taken to a veterinarian then if possible taking a stool sample will be very helpful. The stool can be placed in to a clear plastic bad or zip lined plastic food bag.