Just For Men Hispanic Shampoo-In Hair Color, Darkest Brown, #4931 - Kit Looks Natural - Just For Men targets only the gray hair. Replaces it with subtle tones that match your own natural hair color. Fast as Shampooing - Ammonia-free formula works in 5 easy minutes. Rejuvenates Hair - Vitamin-enriched. Leaves hair thicker and fuller-looking. Ammonia-free formula would not damage hair. Lasts Up To Six Weeks - Lasts until the gray grows back.