Just For Men Hair Color Darkest Brown 50. 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 won't damage hair. Lasts Up To Six Weeks. Lasts until the gray grows back. Just For Men comes in 11 natural-looking shades. So, it's easy to find one that truly matches your natural hair color.