Grey hair can actually look yellow or green on some people. To neutralise the yellow colour and leave your hair shiny, use a greying shampoo that contains a violet-based colour. Grey hair often becomes dry and brittle because of the reduction of natural oils, so use a good leave-in conditioner at least once a week to restore moisture and help soften the texture.
If you're not ready to go grey, a new hair colour can hide a few grey strands or lighten an entire head of hair. Avoid anything that's more than two shades lighter or darker than your natural hair colour, or you'll wind up looking older than you are. If you don't want to go back to your natural colour and are enjoying your grey, you might want to enhance your hair with one of the new "greying" colours available.
Adding highlights or lowlights can disguise any grey you want to hide by blending them into the rest of your hair. As with hair colour, avoid lightening more than two shades from your natural colour.