What is the ruling on selling black dye and other hair products to women's beauty salons, and is this earning lawful or unlawful?

Scholars have differed regarding the ruling on dyeing hair black. The preponderant opinion is that it is forbidden for both men and women, due to the generality of the evidence. Accordingly, it is not permissible to sell black dye to anyone known or presumed to be intending to dye their hair with it. As for other colors and other preparations, their sale is permissible, subject to legitimate Islamic guidelines.