The contemporary scholars differed concerning the ruling on lightening the eyebrows. Some of them said it is not allowed, as stated in the answer of the Standing Committee to the following question:
Recently it has become a common practice among women to lighten the eyebrows; they dye the top and bottom of the eyebrows so that they look as if they have been plucked and thinned. This is obviously done in imitation of the west. The substance used for dyeing is also dangerous to the hair from a medical point of view. What is the Islamic ruling on doing such things?
After studying the matter, the Committee for Issuing Fatwas replied:
Lightening the top and bottom of the eyebrows in the manner mentioned is not permissible, because it is changing the creation of Allaah and it imitates the plucking that is forbidden in sharee’ah, because it achieves the same effect. The prohibition is even more emphatic if that is done in imitation of the kuffaar or if using it causes harm to the body or hair, because Allaah says (interpretation of the meaning):
“and do not throw yourselves into destruction”
and the Prophet (peace and blessings of Allaah be upon him) said: “There should be neither harming nor reciprocating harm.”
And Allaah is the Source of strength.
Fatwa no 21778, dated 29/12/1421 AH.
Shaykh ‘Abd-Allaah al-Jibreen (may Allaah preserve him) said:
I think that it is not permissible to use these dyes and change the colour of the eyebrows because the Prophet (peace and blessings of Allaah be upon him) cursed those who pluck the eyebrows, those who have that done, and those who change the creation of Allaah. By His wisdom Allaah has created differences in eyebrows; some are heavy, some are fine, some are long and some are short. This is one of the ways in which we can tell people apart, and know each person by his own characteristics. Based on this, it is not permissible to dye them because it is changing the creation of Allaah.
Fataawa al-Mar’ah, compiled by Khaalid al-Juraysi, p. 134.
So this is an area concerning which the scholars have differed.
But it is better and more on the safe side not to do that.
Those who are qualified to engage in ijtihaad should do what they think; those who are qualified in the area of tarjeeh [comparing opinions and deciding which are more likely to be correct] should do what they think is most likely to be correct; the ordinary people should follow the trustworthy scholars in their own lands or those whose fatwas reach them.
And Allaah knows best.