@burcinc-- As long as you don't use hair dye on your beard, I think you will be fine. Just do a little test on a small part of your beard to make sure that you're not allergic.
I use a regular store brand, beard dye for men. I haven't had any problems with it. If my beard was gray, I would actually leave it as is but mine turned full white, while the hair on my head is still brown.