Please include where you live and what garden zone. Did you buy these at a nursery or a florist shop? How often do you water? Do you have mulch on the soil?

Thanks for the reply. I am in CT, zone 7, bought at a nursery. The ones in the planters are from same time and place. There is new mulch as of spring and watered every other day.

Hydrangea flowerheads can become discolored if the blooms are finished, they have been somehow damaged/bruised during transport or planting, if they have been scorched by sun or if they have had too much water directed on them. It is not a disease or insect problem but just something that occurs due to one or more of these factors. You can just remove them if you find the appearance unsightly but I wouldn't do any other pruning except just the deadheading, if you so desire.

+1 for spent blooms. No single bloom on anything lasts all summer; it's not plausible!!

You're caring for them just fine though, keep it up! Prune or deadhead anytime around now.