Chapter 4 143 of the precursors leads to dark brown chromophores. The difficulties include stability of these actives in air as well the limited range of colors that they form (mainly brown shades). The product development has been limited mainly to men’s products, where only a low level of color is required and only natural shades are tolerated by consumers. Metallic Dyes As with natural dyes, metallic dyes are rarely used today. In the past both lead and silver salts were used but only lead salts are commonly used today. The products contain lead acetate and a sulfur source. Reaction of the lead acetate with thiol grops in the hair produces lead sulfide, and oxidation produces lead oxides that have a gray/black color. The product must be applied daily to Madder Root (red) Chamomile (yellow) Indigo (blue) Henna (red) Cochineal (crimson)