Couple of thoughts.......avoid any overhead watering. When you need to water, do so at the root zone and do so thoroughly. Excessive water on foliage can lead to fungal diseases and leaf spotting. Second, you may have over-amended. Soil conditions radically different from those the plant was grown in can lead to shock. Ideally, if amending is required, it should be done over the largest possible area, never just the planting hole. And never a good idea to fertilize immediately on planting - the plant can't metabolize it. The good news is there is nothing wrong with your plants. The purple-brown coloration is just a reaction to cold, common to many plants, especially if not acclimated to the area or with more foliage than established inground plants may have. The spotting may be just a touch of leaf spot but nothing to get concerned about. Just change your watering methods and pray for warmer weather :-))

Are the stems a ruddy color? Sounds like Preziosa to me. Lowe's is selling a ton of them right now I've noticed. Another thing I've noticed about hydrangeas is that when stems and leaves are colored like the blooms, it tends to keep the blooms in the same color range in a wider variety of soil types. Check out this vendor's picture for accuracy: http://www.hydrangea.com/shopping/pgm-more_information.php?id=34

What Luis said about both soil pH and the compost and composted manure to improve soil texture and nutrient value. I have turned the compost/manure in when creating some beds and just left it on the surface in others, covered by mulch. Where I live is sand of varying texture from a glacial lake, so I have gotten manure from the local dairy farm (fewer weed seeds) and from the horse farm down the road, which is free and since I cover it with mulch, weeds tend not to sprout. You can also get commercial compost either by the bag (more expensive per volume) or by the truckload. What you don't want to do is to only amend planting holes since the change in texture at the edge of the hole creates problems for water movement through the soil. In sandy soil, it often means that the plant dries out. I usually put a layer at least 6" deep prior to installing a bed with shredded wood/bark mulch on top to keep down the weeds. If it's going to be perennials I am more likely to turn in the amendments over the entire bed since they have smaller root balls and I want them to have roots in soil, not just the compost.

Slope planting can be a pain. I planted an ES above my drip tubing and it dried out before I realized that the tubing -because it was lower in the slope- was not giving it enough or almost any water. Sigh.... Duh.... Wilting occurs when the leaves loose moisture faster than the roots can absorb more water. Thus, the hydrangeas can get wilted when heat stress goes up. Typically, temperatures above 85F trigger this; or windy weather triggers wilting but, you could get some wilting indirectly from other sources, such as when sunlight bounces/reflects off nearby windows or walls. Or when your plant has a small root system because it has not been established in the garden yet. Wilting is an issue that lasts until well into the Fall months here (temps still in the upper 90s to 100s here) but your temps are now slowly starting to top off at the 80-degree mark or less. So temps should not be the cause of wilting if they continue just going into the 70s. To tell if the problem is lack of water, insert a finger into the soil to a depth of 4" and water (around a gallon for a newly planted shrub) if the soil feels dry or almost dry. Water early in the mornings. Water only the soil and never the leaves to prevent fungal issues on the leaves. To tell if the problem is not enough (or too much) water, water the plant and then determine how deep down the water got down to; you want the watering to reach down around 8" deep or so. Check several spots around the plant, not just in front of the plant or just on one side of the plant.If you detect that the soil is getting wet much below 8" deep, water less. Remember to go back to Spring watering amounts as soon as Fall temperatures arrive and they remain well below 85F most days. To tell if it is too hot or too windy, check the weather forecast (choose a website that gives you past statistics too) and make sure that the plant has 2-4" of organic mulch (no rocks). Temps above 85F usually start to trigger heat stress. End of season indicators include browning of blooms, lots of yellowing/falling of leaves and change in color of the stems as they harden in preparation for winter. Most macrophyllas have leaves that either turn shades of yellow or light tan to brown (a few varieties like Lady in Red have leaves that turn like oakleaf hydrangea leaves). Some paniculatas turn a medium yellow. Oakleaf hydrangea leaves turn reds, purples, browns, yellows, oranges, a nice feast of Fall colors.Paniculatas tend to loose some leaves via yellowing aduring the summer months. Nothing like half of the bush, mind you; maybe enough so you can see the lower/bottom parts of the stems. I would not necessarily "compare" the ESs to other hydrangeas that were planted at the same time because their root system may be quite different and you cannot "see" if the roots are too small yet, similar enough to absorb large amounts of water quickly. Paniculatas have smaller leaves so they tend to need less water, they loose less moisture than macrophylla's large leaves and they suffer less when under heat stress. A year-old plant is probably not established well (yet) in the garden. Some might be but it can take from 1 to 3 years.