Blonde Look for White Hair
A: We use the term "percentage of gray" to measure the ratio of pigmented to unpigmented hairs on the scalp. So, when someone's hair is 100% gray, it means that all of the hairs lack pigment of and are therefore a translucent white in appearance.
Even the lightest "blondes" have some pigment in them, and starting with a purely gray base, you will need to add toning colors to create a blonde look. The problem is: if the hair IS 100% gray, adding a single shade of blonde will only create a very flat-looking color. Natural hair color is the product of multiple strands of slightly varied shades together reflecting and refracting light.
In order to get a natural-looking result in 100% gray hair, you want to use a base color of the lightest shade you desire, and then apply lowlights of two or three additional shades using a foil application method or similar, to build depth and dimension to the color.
Be aware that gray hair often has a tighter cuticle layer and is resistant to penetration by moisture, and therefore, chemicals. You should look for color additives to use with your color (such as "Gray Magic") at your beauty supply store or else use a pre-softening step before attempting to color the hair. Presoftening involves using a peroxide developer on the hair for a few minutes to help the hair open up to better absorb the hair color formula.
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See also:
The different shades of gray hair
How bleaching hair works
Why how and how hair turns gray
How to deal with color resistant gray hair