Colour the hair and the eyebrows grey using Grimas Water Make-up (Pure). For very dark hair; you use white otherwise use grey. For the head hair you use a sponge or a toothbrush; for the eyebrows or a moustache you use a (artist's) brush.
Hint: if someone has expressive dark eyelashes or is very young, you can make the eyelashes 'colourless' by applying a little Water Make-up (Pure) to them in a light skin colour.