Courtney

“Of the possible shades of indigo dyeing, a deep navy blue was employed most frequently. As a result, ko-ya, the name of the dyers who used it, became a kind of synonym for the whole hand-dyeing industry. The demand for navy blue kept ko-ya so busy that they hardly had time to dye their own clothing; this gave rise to the phrase “a ko-ya who wears white,” which referred in general to anyone too busy attending to the needs of others to attend to his own.”
― Sadao Hibi, The Colors of Japan: Background, Characteristics and Creation