Just For Men Mustache and Beard M50 Darkest Brown is a brush-in color gel designed to eliminate gray hairs in facial hair, providing a natural-looking and fuller appearance. Formulated specifically for coarse facial hair, this ammonia-free dye works in just 5 minutes and lasts until the gray grows back. The formula is enriched with biotin, aloe and coconut oil to nourish and condition facial hair during coloring.