You are totally correct in your statement that the colors you used come out blonde on gray hair. Most all colors come out a shade lighter on gray hair, so the dark brown will be a medium brown on gray hair. If the dark brown is too neutral, try mixing it with equal parts golden blonde warm. Apply full strength(equal parts color and developer) to the new growth. Let it process with a cap for at least 35 minutes. Then take your remaining color mixture and dilute it by half with water to apply to the previously colored ends.(Try to use distilled water or reverse osmosis water if possible)Let the diluted formula process on your ends for 10 minutes. Then shampoo and condition with a color safe product.