My hydrangeas are not as bright blue as they use to be. Why?
Why Are My Hydrangeas Losing Their Bright Blue Color?
Certified GKH Gardening Expert
I suspect that either the aluminum in the soil is getting low or the pH in the soil is going up and they are beginning to fade into the pink side. This article will help you regain their color: https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/change-hydrangea-color.htm