Muji is a general name for single-color Nishikigoi that have no patterns on their bodies. Typical Muji varieties include the yellow-bodied Karashigoi, the bright red Aka-muji, the austere brown Chagoi, and the pure white Shiro-muji. Especially, it is not unusual to see Karashigoi, which are larger in size, exceeding one meter in length, and their performance at koi-shows is remarkable. Matsuba, whose scales are colored black one by one, is also belonged in Muji, and there are Aka-matsuba and Ki-matsuba.
In the Muji category, Koi that are evenly colored all the way to the tips of the pectoral fins and have a good body shape are highly valued.