When covering gray hair, is it necessary to add gold to the color formulation?

When working with any deposit-only system, it is necessary to replace the warm pigments that are missing from gray/white hair for the most natural color results.  The NE Series can be used alone for gray coverage, but adding the DE Series will result in a softer, more natural color.  The HCE Series can be used alone for beautiful warm brown results on gray hair.