Dennis Bernard Gray Oxidizing Drops are designed to be used in any manufacturer's color to cover resistant gray hair. Permanent, demi and semi-permanent color performance is improved by adding this product into the formula. Gray Oxidizing Drops are compatible with all shades of color and with all Dennis Bernard Powertools products. Adding 3-5 drops to shampoo refreshes red and warmer toned colors. As with all Dennis Bernard products, Gray Oxidizing Drops are color friendly, helping to lock in hair color and to prevent color fadeout. Guaranteed!