Use warm water and brush to remove these stains from your dog's beard. Take liquid soap that is available in the market according to its skin. Gently rub the place with brush and soap where you find stains. It will really help you reducing stains in few days. Do it for a week at least. There are some products available in the market like "Angel eyes" that can be used to remove these stains. It really works if you continuously use it. I recommend you to change your dog's food as well. It can be one of the reasons of dog's tears. Some dog stores have special type of liquid that can be used for removing such stains.
Sorry I have no idea I have same problem with my dog as she keeps going under the bath by all of the old pipes
I think that the safest way is to trim or cut that part of his beard. Other things he can wash off and get in to his system. More than likley it come from drool when they drool on them selves of it can come from constant licking. If yo can reduce or get that to stop then the brown will probably go away.
Likely match There