Try a Complements Gel Bath technique. Here’s how:
Mix 2 oz. Complements Lightening Gel, 4 oz. 20 volume developer, 1 Lightening Activator. Add 2 to 3 pumps of shampoo. Apply this formula to the dark areas. Continue to lather through the hair. Let it process up to 15 minutes. Let the hair lighten until the orange stage. Rinse, shampoo and towel-dry hair. Apply a long-lasting semi-permanent color at least 2 Levels lighter than the color desired. Process until desired result is achieved.
You can try an all-over glaze to take the "edge" out of the blonde hair. Use 2 oz. 10GB Radiance Color with 2 oz. of Color Infuser for 5 minutes, or try 2 oz. 10N Complements Long-Lasting Semi-Permanent with 2 oz. Color Prompter up to 15 minutes.
Make sure you are formulating a deep enough color to cover the gray completely. Your best gray coverage formulas will be Level 8 - Light Blonde and deeper, and should have a neutral base. You can also try Miss Clairol GrayBusters,which is specially formulated for resistant gray. Mix with equal parts 20-volume developer and process up to 45 minutes.
Remember, gray hair will take on the exact Level and tone of the color applied, so the more gray hair and the brighter the color, the brighter the result. You must balance the formula by adding at least 1/2 to 1 oz. of a color with a neutral base to the formula at the same or similar Level.
If you are using a permanent color, always use a blue or blue-violet base to counterbalance the warmth, and formulate the color no lighter than 2 Levels from the natural color. Use a long-lasting semi-permanent in an ash base to refresh the ends.