Definetly helpful if you link an image.
Ok here a stage trick that will work for short hair.
You need to get hair paint that is pigment rich.
You start by styling you hair stiff into the shape you want with hairspray or Got2b Spiking Glue.
In this case I would go with the Spiking Glue and mix a bit of the balc paint into the paste while styling first.
Once it's set up you paint the exposed layer of your hair black.
For the beard you can also mix a tiny bit of the spiking glue into the paint and comb the mixture into you beard.
Once you hair and beard is dry go back in with a small bottle of white hair paint and paint a few strands of hair white. His beard have more grey hairs then his hair.