A beard may have different shades of colors. Many men have patchy gray or yellowish beard. With a beard color you can get a more uniform look of your beard, which makes it look fuller and more marked and distinct.
It is also common that men color their beard hair to fit the hair on the head. Unfortunately it does not work so good to use the same coloring as for the hair, which is of a different nature. Just For Men has developed special colors that are customized for beard hair. If you want the same color on your head for the beard, buy the same shade from the same brand.