Beard transplant: Why are hairs on my beard/moustache turning blonde and getting thin?

You can theoretically harvest donor hair from your pubic area for a facial hair transplant.  It is unclear why your hair is turning blond.

losing density in the beard is a result of genetics and could possibly be a sign of alopecia areata. the hair is likely turning blonde due to genetics as well. for a facial hair transplant, using scalp hair is the best and most natural result, but you can also consider using body hair as long as the texture and quality of that hair matches your beard.

Your beard may turn to blonde under exposure of sun .We dont observe lack of density of beard after propecia use ..you may use scalp , chest or other body hair as a donor for beard restoration.

Most changes in hair color/density/caliber over time are the result of family genetics.  Yes, one can use pubic hair for hair restoration to the beard.

I can't tell why your beard is turning blonde. Do you have blonde hair as well?  Yes, you can use pubic hair as a source for beard hair,.