Well, there is a gray mold that sometimes gives such a look but check first for symptoms as I could not tell from the pictures: the flowers develop a "water soaked" look that enlarges to brown patches; the blooms then develop a wilted look (I would not say that yours look wilted... yet); you would also see the mold develop in the sepals (I could not "see" mold in the pictures). If you notice these symptoms, discard the blooms in a plastic bag and throw them in the trash; do not water the blooms or leaves.

Most likely, hopefully, this shrub is not established in the garden yet and could be either having trouble with sunlight, getting overhead watering or the blooms are getting old. I assume it was already blooming when you got it and you do not know when it started blooming?

If the blooms are old, the sepals may be starting to turn green/pink colors and-or get pink/green spots. Pink spots in white blooms usually happen after the blooms are a little old. Hard to say exactly how these spent blooms may change without knowing the name of this variety. Browning of the sepals may be an age, watering or sun issue.

Make sure it gets morning sun only and water only the soil, never the blooms or the leaves, as that promotes spots in blooms/leaves. Maintain the soil as evenly moist as you can and -now and then- make sure the pot's water exit holes are not clogged.

While this same information is there in Luis' post let me just simplify by saying there is nothing wrong with your plant!! The pink spots are not "killing" it - they are just symptoms of the flowers going over. By that I mean, the flowers are aging and white flowered plants will often take on red or pink tones as the flower matures and start to die. Same with the brown areas. This is often exacerbated by overhead watering.

White H macrophylla don't do well at all in more than 1-2 hours direct sunlight (excluding EARLY mornings). I have two several F&E White Outs under my north facing back deck that get these very dabs of sun and the edges turn brown quite rapidly.

I used to have them on my south-facing front porch and they went brown a lot faster (like 2 weeks). In the new location they last about a month longer.

If you're able to get these into an exclusive bright shade scenario, I think they'll fare much better for ya.

Thank you all for the advice! They do see direct sun from about noon to 4 as well as receive water from above when my yard sprinkler runs in the morning. Sounds like I need to move them to more shade and away from where my sprinkler hits them.

Also, a month is a fairly normal time period for individual hydrangea blooms to keep the initial color. They don't last all season, though shade and watering the soil will give them their maximum time of looking good.