I assume you mean the bloom color is originally grayish? I have heard of neutral or near neutral pH in soils causing similar color shade issues with Nikko Blue and others. If that is the case with you, you could try amending the soil with either sulphur (for better blues) or garden lime (for better pinks).

yes thank you,

is there a recommended time to add sulphur for a better blue

Any time is a good time, provided your soil has not frozen in winter. You need to amend the soil based on the information in the label of the product that you get. And do not forget to amend the soil because soil pH reverts back to its original value if you stop amending (not immediately, mond you but it slowly reverts back).. Obviously there is nothing you can do but stop in winter if the soil has frozen but, at other times, try to follow the application frequency in the package.