There may be some leaves that show a little of watering issues (not enough, pm) but for the most part, it looks like a pest is at work. I could not notice any on the pictures. Check the top and bottom at day/night for signs of aphids, lacebug, scale or whitefly. If the damage does not appear to be increasing (take pictures of the same leaf or leaf section) and you detect no pests for several days then assume that the culprit has already left (apply controls early next year if you id them then).

Stick your finger into the soil right next to the plant. Is the potting soil dry?

Check for spider mites.

White fuzz looks like powdery mildew

Thank you all. So...other than watering, should I just spray some pesticide on them?

No. Pesticide is a general term and just throwing chemicals at a plant may do as much harm as good since there are critters that help keep pests in control as well as ones that cause harm. You might want a miticide if you actually find mites or you could just give them a good solid spray of water under and over the leaves for several days since spider mites like it dry. If you spray an insecticide or a fungicide on mites, it will do nothing. You could try spraying a fungicide if someone is sure it is powdery mildew, though I don’t think it is and I haven’t seen a definitive answer. A fungicide won’t get rid of a current mildew problem, but it might prevent it from spreading to new foliage or the other shrubs. Until you have a firm diagnosis, there is no reason to try treating a problem that you haven’t IDed for sure. I would take a sample branch (cut and put in water to keep fresh) to the nursery where you bought them to see if they can ID the problem in person. Or see if the folks at the nearest Cooperative extension can figure out.

We haven’t gotten any answers from you as to whether you found other bugs when checked again (and you want to check with a flashlight after dark as well as daytime) or any response to comments about water amounts. So it really is too soon to apply pesticides since you don’t heat know what the issue is.

Often though not always, plants are more susceptible to disease and insects for their needs aren’t well met. Where are you located generally and how much sun do the plants get? Is there at least an inch or three of mulch under the shrubs? Is their grass growing under them? Did you spread weed-n-feed on a nearby lawn this spring? What was the result when you checked the soil moisture, both around the plant, but also in the original root ball/potting soil?

ETA: Luis and I cross posted but we said quite similar things though he was far more clear.

spider mites and lace bugs cause that pale "frosted" look of the foliage. I do not know if lace bugs will bother hydrangeas where you are (they don't here in the PNW so far anyway, at my house it's azaleas and rhodies only) so spider mites are likely. You don't ever want to just spray pesticides, herbicides or fungicides without a firm diagnoses. they are poison and some persist in the environment for a long time.

Thank you to everyone who commented. I confess I don't know much about various pest types so I wouldn't know a mite if it bit me. Time for research! As to everything else, I am in Northern Va, zone 7. These plants are in the flowerbed in front of the house and are mostly in the shade but get 2 to 3 hrs of sunshine in the late afternoon. Only one of the three seems to be affected, and the other two are growing very nicely (although I see some minimal similar damage on the healthy plant next to the affected one.) Nothing else in the bed seems to be affected. My attitude to plants is mostly benign neglect (except occasional watering) so I haven't fertilized, weeded or mulched this year and they seemed to be growing nicely until this point. I've just looked at the leaves from the top and bottom and didn't see any pests. I do think it's pest damage because leaves have holes in them that's clearly the work of something. So it's not just under-watering.

Many pests hide during the day so also check sporadically at night. Of course, this would not apply to fungal issues.... ;0)

They are so close to the structure!!

Are they under eaves? Do they receive natural rainfall?

Do yourself a favor and move them out several feet while they are still small.

Limelights get quite large- in their current location you have really set yourself up for maintenance nightmares

Fungal disease