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.
References
Blue rinse Wikipedia(Text) CC BY-SA