Jabir reported that when Abu Qubafa (father of Abu Bakr) came in the yeu of Victory or on the Day of Victory (to the Prophet to pledge his allegiance to him) his head and his beard were white like hyssop. He (the Holy Prophet) commaded or the women were commanded by him that they should change this with something (that the colour of his hair should be changed).  

أُتِيَ بِأَبِي قُحَافَةَ أَوْ جَاءَ عَامَ الْفَتْحِ أَوْ يَوْمَ الْفَتْحِ وَرَأْسُهُ وَلِحْيَتُهُ مِثْلُ الثَّغَامِ أَوِ الثَّغَامَةِ فَأَمَرَ أَوْ فَأُمِرَ بِهِ إِلَى نِسَائِهِ قَالَ غَيِّرُوا هَذَا بِشَىْءٍ  

Change it with something but avoid black.  

أُتِيَ بِأَبِي قُحَافَةَ يَوْمَ فَتْحِ مَكَّةَ وَرَأْسُهُ وَلِحْيَتُهُ كَالثَّغَامَةِ بَيَاضًا فَقَالَ رَسُولُ اللَّهِ ﷺ غَيِّرُوا هَذَا بِشَىْءٍ وَاجْتَنِبُوا السَّوَادَ