I did some internet searches to find out if there is anything you have to do differently for gray and white hair. There are a few good tips out there. The #1 thing I read over and over was DO NOT use high heat styling aids on your hair. It will make it turn yellow!
My stylist told me to buy Clairol Shimmer Lights shampoo and conditioner to use once or twice a week. It cleans the yellow and other impurities (minerals from hard water, cigarette smoke, etc.) out of your hair and enhances the color. It does have Violet #2 in it, so if you use it every day you will have 'Blue Hair' - not a look I believe any of us are going for!
Speaking of blue hair; I read a post by a young girl who said she thinks the trend of short, gray hair on older women is the 2000's version of the curly blue perm of the 1900's! Brat.