Some hydrangeas have blooms that change color widely thru the season. My macs tend to go from pink to green to brown. But brown is something I usually see by the Fall, not this early.

For that reason, I am going to suggest that you consider that the hydrangeas are getting too little water and/or too much sun.

Be aware that newly planted hydrangeas will require more water than established ones so be ready to water more than once a week during the summer. 1gallon of water per week is OK here in Texas for new 1gallon nursery plants in the Spring. By the time we get to August, I have to double/triple that.

Wilting of the leaves lets me know that more water is needed. Browning of the leaves lets me know that the plants are getting too much sun.

Feel free to do some deadheading if it seems necessary but I would be very careful starting next month. That is when we could accidentally prune away next Spring's blooms on plants which bloom on old wood.

Luis