in the middle of your darkest and lightest color of your hairs to color your hair for no more than 15 min. The hair color should be nonpermanant, no ammonia, as organic and natural as possible. Repeat every 1.5-2 months, depends on how fast you hair grows.
It will create a multi-color layers which make your hair looks richer, natural with high light effect. When the color fade out, the older white hairs acturally will absorb colors from environment. If you use slightly yellow colored conditioner or hair oil, they will look like light sandy yellow color, sometimes even golden yellow.