Baby Blue hydrangea

 I bought three Baby Blue hydrangeas which all looked like the one above.  Unfortunately, two of them now look like the one below.

The same thing has happened to two of the three pink hydrangeas I planted at the same time.  They have all been treated in exactly the same way, except the pink ones are planted in JI3 and the blue ones in Ericaceous compost. They have not been under- or over-watered to my knowledge, and as the other eight or nine hydrangeas in the garden are doing well, I'm baffled. .