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It is likely lacking a good phosphorus/nitrogen balance in the soil. Too much nitrogen or too little phosphorus will cause it to fail to bloom. This article will have some other suggestions as well:
https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/hydrangea-not-blooming.htm

They could have been lacking water, as the rainfall you received was not much. Hydrangeas are heavy water feeders and if they do not get enough, will quickly succumb to dry conditions. This article will help determine if your shrub is still alive. In the meantime, give it some water. https://www.gardeningknowhow.com/plant-problems/environmental/how-to-tell-if-a-plant-is-dead-and-how-to-recover-an-almost-dead-plant.htm

This article has information about changing hydrangea colors: https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/change-hydrangea-color.htm

This article should help: https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/growing-hydrangeas-hydrangea-care-guide.htm

You don't say where the black is on the leaf. If its around the edges, you plant is suffering from transplant shock, sunscald (because it was grown in a shadier spot than yours) or lack of water (possibly before you bought it). If this is the case, your plant will recover. If the dark spots are in the center of the leaf, it's probably disease. Dig it up and return it to the store.

Your hydrangeas probably just need a rest. It's commmon for these plants, the 'old-fashioned' varieties at least, to flower heavily for a year or two and then rest for a season. If you didn't have a late frost that would damage the forming buds, I suspect that's the answer. If the problem continues, you'll need to see if they're getting as much light as they used to.