All perfect praise be to Allah, The Lord of The Worlds, and may his peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
Dyeing eyebrows with a color like that of the skin aims to hide their true shape in order to make them look thinner and more beautiful. This technique can also be done to the upper and lower sections to make the mid section look thinner. If this is the case, and the eyebrows weren`t plucked, there is no harm that married women use such dyes to beautify for their husbands, provided that it was medically proven that they are harmless, because the general principle in such matters is that it is permissible unless there is evidence (daleel) from the Quran or Sunnah stating otherwise.
In fact, the prohibition pertains to plucking the eyebrows, not to dyeing them with different colors. However, it is disliked for an unmarried woman to apply these dyes in order not to cause temptation. On their part, Muslim jurists have stated that dyeing the hands and feet with Hena is disliked for the unmarried woman, as stated in [Moghni Al-Mohtajj,(vol.1/pp.407), and other books.]
By analogy, this rule applies to dyeing the eyebrows for the unmarried woman. And Allah Knows Best.