Reference: http://www.alfawzan.af.org.sa/node/15916
Question: My sister lightens her eyebrows, as well as her face, so what is the ruling regarding that?
Response: It is not permissible for her to do that. She should not interfere with her eyebrows [in any way]; she should leave them just as they are, without plucking them, or cutting them [in any way] or dyeing them, rather she should leave them just as Allaah سبحانه و تعالى created them.
