What is "blue rinse"

n. A diluted blue hair dye used to reduce the yellowed or translucent appearance of greying hair on older women (because the ability to see the colour blue decreases with age).

A blue rinse is a dilute hair dye used to reduce the yellowed appearance of grey or white hair, typically associated with older women. In a manner similar to laundry bluing, the blue rinse can make yellow-white hair appear blue-white.

The blue rinse gained popularity after Jean Harlow's appearance in the 1930 film, Hell's Angels. Queen Elizabeth also contributed to the popularity of the blue rinse in the 1940s.