Neither disease.
What's the rest of the plant look like?
If possible, please post a picture.

Cercospora....

Here is a link that might be useful: Cercospora on hydrangea

Thank you both for your responses.

Jean001, I'll try to get a pic of the whole plants (have to borrow a camera again), but they all look good besides the leaf discoloration. They're producing nice flowers, growing well.

ians_gardener, thank you for the link! The photos look exactly like what is going on with our hydrangeas. I'm betting that top-watering is the problem. If I'm surmising correctly, there isn't much to be done other than to talk to the manager about the need to stop top-watering, and wait for it to clear up? Should we remove infected leaves?