https://www.medicalnewstoday.com/articles/323147#stool-colors
This should help. The fact that you only notice this during a fast is rather interesting. I wonder if you have Giardiasis that hasn’t been caught. Fasting might make it stand out more. I would consult a doctor about this to be on the safe side. It can be a number of issues.
I water fast 4-7 days per month.
During the last few days of fast, my bowl movements are liquid gold, and I love it. My system is cleaning. 1 day after consuming foods I’m back to award winning, beautiful textured bowel movements.
I had my gallbladder removed 2 years ago.