How old is your kitty?
No worries. I too have a solid black cat. Cats all shed their whiskers from time to time just like the rest of their fur. Whiskers are nothing more than sensitized hair shafts that actually connect to the muscle around the muzzle and eye brow area.
When they get ready to shed a whisker they often turn white or gray. They will naturally do this too as they age. Much like people get gray hair.
Let me know if you need any further help with your furry baby.