I'm going to post a comment I found on a chemistry youtube video. Basically the youtuber made a joke about how chemicals often turn yellow after reaction and a commenter explained why in chemistry terms.

"Regarding 13:23 - I'm sure you already know it, but for anyone who wonders: many organic stuff are yellow because they have a lot of conjugated bonds in them (in the case of the imine here the bezene ring is conjugated to the nitrogen via its free electron pairs). This causes the electronic excitation energy to drop, bringing it from the close UV range into the visible range, i.e. the molecule absorbs deep-blue/violet photons, and we're left with a yellowish-looking product."

Which in all honesty I don't know how applicable this is to the urine we produce but was interested if anyone could confirm or deny it for me here.