Hello and thankyou for approaching DoctorSpring with your query.
Green stools is nothing to worry and can happen as a result of your diet. If you have eaten something green like spinach, food coloring as in flavored drink mixes or ices pops. Certain medications like iron supplements are also known to cause green stools in some individuals.
Another cause of green stools can be due to the food moving too quickly through the large intestine as in diarrhea, or as a result of large amounts of unprocessed bile in the intestines. As a result of this the bile does not break down completely and gives the stools a green color.

I would suggest you notice your diet for any particular pattern, like your stools are green after a particular meal or are you on any medications.
This is unlikely to be due to thickening of the gall bladder.

But if you have signs of abdominal pain, nausea, vomiting, loss of appetite, weight loss or fever you will have to get evaluated. You will require to get an abdominal ultrasound.
As of now you have nothing to worry.

I hope this has helped.
Thankyou