Hydrangea

I have 3 of these plants in my garden and they all sit alongside one another alongside the house.

I understand that their blueness or pinkness is dependent to a large degree on the soil acidity...........

....so why are mine white, one with a hint of blue and one with a hint of pink?!?!? They used to produce gorgeous blue blooms but the past few years have been looking progressively more and more anaemic.

Must google it sometime.