What causes the blue color in blue diaper syndrome?

Answer 1

I had never heard of this before so I did a search and I found this information: Blue diaper syndrome is a rare, genetic metabolic disorder characterized by the incomplete intestinal breakdown of tryptophan, a dietary nutrient. Symptoms typically include digestive disturbances, fever, irritability and visual difficulties. Some children with blue diaper syndrome may also develop kidney disease. Infants with this disorder may have bluish urine-stained diapers. Blue diaper syndrome is inherited as an autosomal or X-linked recessive trait.

Answer 2

It's a chemical reaction