Depends on how far you want to go - too far and you loose the character.
Here is what I did.
Opened in Camera Raw and did a white balance tool click on grey area of beard.
Created a new blank layer.
Used the color sampler eyedropper to select the skin color of a good patch of skin.
Switched to Brush tool, used a soft brush and set the brush opacity to about 30%
Clicked on the new blank layer to paint color back into the areas I thought you might be trying to fix. (Guessed)