You can but that sounds like the dog has lost the pigment in it's hair and that is nothing wrong with the dog. Or if the dog has a nerve condition and it lays and licks its feet it will lick the pigment out of its hair and the hair will turn a funny red color.
Your dog has been licking it's feet and the staining on the beard is caused my saliva also. You could try a whitening shampoo. I would be more concerned about WHY he's licking his feet. Dogs lick when they are bored, stressed, or anxious. They also lick if they have allergies or may be overdue for his grooming appointment.
I have 2 mini schnauzers and they both get red/brown stains on there face from licking thier beards after eating. It is from thier saliva. I use a whiteing shampoo and it dose the trick. One of our schnauzers licks her paws, which will cause the stain as well.