Traditionally, Japanese women wear a kimono during a tea ceremony.
In formal Japanese tea gatherings, women commonly wear a subdued kimono, often an iromuji: a solid-colour, largely unpatterned garment. Its quiet appearance suits the ceremony's emphasis on harmony, restraint and attention to the tea, utensils and guests. The kimono is worn with an obi, the sash that also helps hold ceremonial items such as the folded fukusa cloth.
Clothing is practical as well as symbolic. The sleeves, collar and obi provide places for carrying or tucking small tea-ceremony accessories, while white tabi socks are traditionally worn by both men and women. Seasonal choices matter too: lined kimono are generally used in winter and unlined versions in summer.
Kimono is the canonical quiz answer, but it does not mean every participant must always wear one. Beginners may practise in Western clothing, and guests at some gatherings may wear formal Western attire. For formal occasions, however, the host is expected to wear kimono, and kimono remains especially important for women studying established tea schools.