When your hair goes gray it is due to the fact that the cells in the follicles called "Melanocytes" no longer generate pigment, the main one being melanin. The hair follicle loses all pigment over time and occasionally goes white. The white against your darker hair give the effect of gray. As your hair is no longer as healthy as it use to be you need to consider treating it to prevent it from going brittle and lifeless.
The vital vitamins that you would need in this case is B12, and Omega 3's. You can take these supplements as tablets or you can use a shampoo that contains these types of nutrients. There are many products on the market that promise to treat Gray Hair or even take Gray Hair away. Beware as there are only a few that will actually be effective.
If you are looking for a shampoo that will replace the lost nutrients then you need to make sure that the ingredients of the shampoo will actually treat the problem. If the shampoo contains Emu oils then you know that the product will work. The Emu oil contained in the shampoo is known as the follicle awakener and has been used by many to help prevent the sunset of gray hair. Every hair must have omega 3's to grow properly. And Emu oil is the only ingredient that we know that can moisturize the hair enough to get it back up to an 8% moisture rate as it is supposed to be.
Now although a shampoo with these types of ingredients will help with the lack of moisture in your hair you may find in some cases it will actually darken the hair and reverse the graying process to some degree. The Emu oil actually works at the root of the hair follicle by penetrating the hair strand rejuvenating the pigment.
Just because you have Gray Hair does not mean you should not treat it with conditioner and shampoo. Gray Hair can look healthy if treated properly. If you use the correct products you will find your hair will be healthy, full of volume and in some cases you could even get your original hair color back.