Dyeing the beard with henna and katam
Question

                Is it permissible to mix red henna with black katam and put it on the grey hair of the beard, noting that after that the colour of the beard will be black from a distance, and from close up it will be clear that the colour is dark brown?.
Praise be to Allah.
    Shaykh Muhammad ibn ‘Uthaymeen (may Allaah have mercy on him) 
    said: 

    The Sunnah is to change the grey hairs by using henna, or 
    henna and katam. If it is changed using henna it will be orange and if it is 
    changed using henna and katam it will be between red and black. There is 
    nothing wrong with that and no sin involved, in sha Allah.