Correct Demarcation in Hair Color
A: It sounds as though you made a common mistake when coloring your hair to cover the gray - namely switching to a lighter color without lightening the starting color of the hair.
You should either select a 30-volume peroxide to combine with your hair color choice, which will lighten the hair before depositing the new color, and may mean you need to select a color from the professional formulas at your local beauty supply store rather than using a kit purchased at a supermarket or drugstore.
You also have the option of simply using a lightening agent to lift the hair color to a shade at or slightly lighter than the color you are trying to achieve before you apply the new hair color.
If I have misjudged your situation and your problem is simply that your new color - while adequately altering the color previously used - has failed to cover the new growth, then your situation is that the gray hair is more resistant and needs to be treated as such.
Gray hair can often be color-resistant. Fortunately, there are formulas designed for resistant gray hair, as well as additives that can be used in any other hair color formula which will help to make gray hair take color better. These can also be found at your local beauty supply store.
Whichever of these situations is the cause of your unsatisfactory hair color results you now have suggestions for correcting them.
©Hairfinder.com
See also:
How to color your hair
Color resistant gray hair
The different types of hair color
Is it safe to color your hair every 2 to 3 weeks, just at the roots?