In Japanese, hikari means shinning and muji means plain. Basically the Hikarimuji class of koi are single-colored, metallic koi. Koi included in this class are Platinum Ogon, Yamabuki (yellow) Ogon, Kinbo (shiny gold) Ogon , Ginbo (shiny silver) Ogon , Orengi (orange) Ogon and Nezu (silver gray) Ogon. All of these koi are solid color koi with metallic sheen. 

This category also includes Kin Matsuba (literally 'golden pine needles,' for individual, glittering scales appearing like raised markings)", and "Gin Matsuba (literally 'silvery pine needles,' for glittering scales on the platinum ground which look like raised markings),"