pepper-and-salt 
adjective
Flecked or speckled with intermingled dark and light shades: his pepper-and-salt beard...
- After the war, her costume ‘is covered, winter and summer, by a frayed macintosh… and she now wears a hat as well - a thing like a basket pulled down over her straying, pepper-and-salt hair’.
- His big problem, as he might admit in the lonely watches of the night, is located just below the pepper-and-salt moustache of which he is so proud.
- I smiled at the face in the mirror, scraped at the pepper-and-salt stubble, and gave myself a very close shave.