Muslim men may use henna as a dye for hair and most particularly their beards. This is considered sunnah, a commendable tradition of the Prophet Muhammad.On the topic of red-haired Muslims we also have two more to add to our list; Oruç Reis and his brother, Hayreddin Barbarossa. Both had red beards and were nicknamed Barbarossa because of it. Hayreddin was an Ottoman admiral of the fleet and Oruç was a Barbary pirate.
Whilst looking into the nickname Barbarossa, quite a common one throughout history (you may remember Frederick I Barbarossa), I came across the fact that "red beard" in German is Rotbart. Rotbart sounds very similar to the name Robert. I've speculated before about the name Robert maybe meaning red-haired. This would run contrary to the accepted etymology, but it would make a bit more sense. Maybe rotbard works in relation to this.