not sure why on earth you'd want to, or why its in the music section, but if its for fancy dress or something like that, then I think sprinkling talcum powder in does work quite well. I remember having to do it for a play once.
You can buy products that will strip the colour from your hair (you don't say how far, you're prepared to go), Superdrug and Boots carry them so if you ask an assistant they should know what you're talking about. The result depends on your natural colour and what effect you're going for.