I could not make out the affected parts up close but they appear to be browned out. Browning of the blooms in the summer on the first 1-3 years suggests that the shrub may need more water. To help dissipate the heat from blooms and leaves, some people temporarily give them shade in the form of a lawn chair or umbrella. In future years, when their root system has grown bigger and can absorb more moisture from the soil, this may not be a problem. If the plant does not get enough moisture, the plant begins to kill the blooms (what you see as brown out) and the leaves could be next. The leaves may show browning of the leaf edges that moves inwards.

I noticed some leaves that had been eaten. It does not seem to be a problem (yet) and I would ignore it but, you may want to keep an eye on that and look for pests during the day and night, especially if that problem is growing.

Lastly, keep an eye on a gray mold that sometimes makes the blooms look as it they were wet, then they turn brown and you see this mold. I doubt your shrub has this but it pays to keep informed just in case.

Thank you! I know what is eating it - these little light green grass hopper looking things. I have sprayed it several times. What is a good product for gray mold?

If. It is mold, you can cut of the blooms and throw them in the trash.

http://homeguides.sfgate.com/treat-gray-mold-hydrangeas-90087.html

Water the soil early in the mornings and never the leaves or blooms.

Here is the dark area close up