Answer: Unfortunately I have not seen this plant myself and am unable to find a standardized description of it, although it is occasionally offered for sale. I am wondering if this is a case of a bloom that is described as "near white" or as "fading to white" rather than as straight white. Hydrangea blooms color can be affected by soil pH, as you saw when you used the Miracid. A somewhat acidic 5.5 should turn them blue, a more alkaline 6.0 should turn them pink with the effect being more intense the more extreme the pH. I do not know of any treatment you could use to turn the blooms white with a possible exception of keeping the soil pH somewhere in between the two and causing any color to possibly fade. If you really want a white hydrangea you might look into the H. arborescens varieties such as "Annabelle" which is truly white naturally.
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