Men in kilts sexy!
Men is urine stained shirts NOT sexy!
Kilts for courting - war for killing.
Hmmm.
My favorite color is Prussian Blue. I was amazed to discover that a major ingredient in the original dye was ox blood (the chemist was trying to get a red...).
If a chemical reaction with urine would get a bold yellow color, believe me, the dyers would go for it.
Urine was also used in tanning leather and quenching iron to make blades.