Grizzled
1. Partly grey or streaked with grey.
2. Having fur or hair streaked or tipped with grey.
Usage is now mostly restricted to descriptions of hair, although the name lives on in the names of some species, eg. Grizzled Skipper butterfly.

Surprisingly the first recorded English usage was as early as 1458. The word is possibly derived from the French grisellé, but the OED says this is lacking evidence.