Definitely not for use on silver hair! I was salt and pepper at the time... the grey coverage was a surprise, not the goal.
I don't know how different your climate is from mine, but you might do better to plant your next rosemary in the ground, perhaps in a protected spot. Potted plants are more susceptible to freezing than inground. My Arps not only withstand winter freezes, they bloom this time of year. I just went out to pick some for tea per Cinda's suggestion; can't recall trying it.
Just now