Iromuji is a type of traditional clothes in Japan which is a plain kimono of color other than black with no patterns woven in.
By adding a family crest, it may also be worn as a formal dress like homongi (semi-formal kimono for women) and the like, and without family crest it can be worn as a casual dress, and furthermore if a black obi (kimono sash) is worn, it can be used as an informal mourning dress; as such, iromuji is a useful kimono that can be worn at any time, place, or opportunity.
Also, if an obi with the width of nine sun (thirty-four cm) of the color of light gray is worn, it can be used at memorial services as well.
In the Kanto region, the type of kimono with the pattern called "komon" (kimono with fine pattern) which is used in the kamishimo (samurai costume, old ceremonial costume) may be used for similar purposes, but in the Kansai region, Edo-komon (fine patterns utilized in Edo) may sometimes be treated as "komon" rather than iromuji.
In sado (tea ceremony), with the meaning of putting off showiness entirely and avoiding clashes with the patterns on tools, it is recommended to wear iromuji during tea ceremonies.