This is denoting hair condition issues. If a colour results as grey and patchy from use of Colour Restore Silver Blonde (which is conditioner based), this is a strong sign damage was present in the hair prior to use of the product. The patchiness indicates colour has being pulled into the hair through aggressive porosity. If you feel the result is very grey, this means the hair was over toned white and likely silver. In such an instance, Silver Blonde will have added to the existing silver tone (present in the hair prior to application) and has intensified to grey.
The first step is to wash the hair several times in a clear or clarifying shampoo. This will flush out some of the excess pigment. The second step is to use Precolour Protein Porosity Spray prior to application of any further colourants. This is because your hair has grabbed colour, demonstrating high porosity. Protein Spray will fill any gaps in the hair, even out porosity and prevent colourants grabbing and evoking patchy or intense results.