It is important to choose the right shade. What is ideal is to use shades of heights 8.0, 7.0, 6.0, depending on your own desire, the above because the darker shades make the root noticeable very quickly.
You must also apply a sufficient amount of product, preferably use the 20-volume developer and leave it to act on gray hair for 35 minutes max. Lastly, it must be remembered that prior diagnosis is very important for optimal coverage of gray hair. With the correct diagnosis, the color professional will be able to make a good selection of the tone to apply and the technique to use.