A lighter shade than the natural color should be used to cover gray hair. Why, because in the process of coloring the gray you are adding color (pigment) to hair that already has pigment, if you don't choose a lighter shade the additional color will darken your hair.
Gray hair is very often resistant to hair color, so do a color test to see if your gray hair accepts the hair color. There are hair color formulas specifically designed for gray coverage, and additives available for regular color formulations to help it to penetrate gray hair.
If you are trying to cover a small amount of gray hair, less than 30%, use a color two to three levels lighter than your natural color. Because all you want to do is cover the gray, you want to use 10-volume developer, which will activate the color without lightening the hair. Selecting a color a few shades lighter than your natural hair color will make the colored gray hair appear to be 'highlights'. A lighter shade also keeps the rest of your hair from getting darker during the coloring process as additional color is deposited onto the hair.
