i Register
In some senses, grizzle is marked as slang, UK. Watch for register when choosing this word.
noun
A dark grey colour.
Grey hair.
A grey wig.
adj
Of a grey colour.
verb
To make or become grey, as with age.
R. F. Burton hardship of the way such as would grizzle little children
Pall Mall Magazine I found myself on the Nubian desert shaking hands with a grizzling man whom men addressed as Collins Bey.