Macrophylla
Hydrangea macrophylla means large- or long-leaved
Hydrangea macrophylla is a species of flowering plant in the Hydrangeaceae family, The crazy thing about these shrubs is the fact that the bloom colour is affected by soil pH.[3][4] An acidic soil (pH below 7) will usually produce flower color closer to blue, whereas an alkaline soil (pH above 7) will produce flowers more pink.
So even when you buy a blue specimen if your acid content is not high enough it could result in a pink flower.