"in POIS my stool tends to become lighter and more yellowish in color". I get the exacly the same symptom and it stays this way many days after the POIS period. I didnt have this the first decades, it arrived during the last 5 years. I strongly belive this symptom it is related to the pancreas or/and the liver, which both lowers there capacity during POIS inflammation. A CT-scan showed that my pancreas were smaller then normal and I will have a liver ultrasound check this spring. Consider this:
"The normal brown color of stool occurs due to the presence of bilirubin. Bilirubin is formed as a breakdown product of hemoglobin (from red blood cells) in the liver and is secreted into the bile, which enters the intestines"
"pale yellow, greasy, foul-smelling stool: malabsorption of fat due to pancreatic insufficiency"
https://www.medicinenet.com/stool_color_and_texture_changes/symptoms.htmThis is just a explanation though, the sollution is still to minimize the POIS inflammation. But there might be a good idea to take pancreas enzymes to get the organ "going" though the POIS days. I've just got pancreas enzymes presciption from my doctor. Maybe you should check the state of your pancreas.
Do you share any of the symptoms of
Exocrine pancreatic insufficiency (EPI)?