Perhaps all flowers are destined to be pink in our garden as it seems our beautiful, once blue, Hydrangea, which you will remember here is turning pink! I guess the existing soil in the plant pot was alkaline after all. To try and reverse the process I have been saving up my eggshells, crushing them up, and adding them to the soil as apparently the calcium in the eggshells will help make the soil more acidic. Let see if this does the trick.
Hydrangeas turning Pink.