WHEN TO COVER THE GREY
If your hair is just beginning to change colour, with the grey making up less than 20% of it, use a semipermanent colour that will begin to fade in about 6-12 washes. For up to 50% grey, opt for a semipermanent that is claimed to last for about 24 washes. Only choose a permanent dye if the majority of your hair has turned grey. If you’re mostly grey, consider a shade slightly darker than your normal colour, because the colour may fade with exposure to sun and shampooing.