Yumean family restaurant is offering ayu or sweetfish tempura using fish caught in Lake Biwako 琵琶湖, Japan's largest lake. Sometimes tempura is dipped into special sauce, but other times it is dipped in salt or a salt mixture. This special offers three different colors of salt. Not other information is provided, but I assume each salt is naturally colored and is separately sourced.
Photo is a web capture for explanatory purposes, copyright belongs to the company.