Looking at familiar bodily fluids for a learning session. At first glance they both look the same. Then I noticed the N=C in biliverdin and HN-C in bilirubin. How can a N=C (imine group) and HN-C (secondary amine) make such a difference in colour? They look like structural isomers of each other to me. Or is there any stereoisomeric differences as well to this colour functional group change?
(Jaundice is directly related to bilirubin, urine is a product of bilirubin, I reckon there must be a real good reason and help aid from the colour change representation.)