It is permissible for a woman to bleach the eyebrows for her husband only because she is commanded to beautify herself for her husband. As well, she is expected to hold her adornment from any foreign men.

If she’s able to make the bleaching seen by her husband only, and no other one, then it is well and good. But if the foreigners are seeing it then it is not accepted

Professor Marzen Ismail Haniyeh, a Palestinian scholar says:

Specifically, the problem is not in dying the eyebrow in shariah, but in the aspect of beauty. It is not permissible for a woman to beautify her face for other than her husband. When she dyes her eyebrows, and goes out like that, she is compared with someone who adorned herself and went out with her adornment, which is not permissible in Shariah.