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It sounds like you have sooty mold. This article should help: https://www.gardeningknowhow.com/plant-problems/disease/how-to-get-rid-of-sooty-mold.htm

This is a fungus caused by pests. I would treat the plant with neem oil. It is effective against the pests responsible as well as the sooty mold. Here is more information that may help you:
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm

Generally, wilting of hydrangea is caused by a watering issue. It may be overwatered. Check the soil and make sure that it is damp, but not soaked. It should have adequate drainage.

This article will help with the green color: https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/green-hydrangea-blooms.htm

It could be either black spot or sooty mold. Both are treatable and, in most cases, not fatal to the plants. These articles will help:
(this is about black spot on roses, but it applies to all plants) https://www.gardeningknowhow.com/ornamental/flowers/roses/black-spot-roses.htm
https://www.gardeningknowhow.com/plant-problems/disease/how-to-get-rid-of-sooty-mold.htm

Typically, in hydrangea, this is caused by a watering issue. Since it's newly planted, there may be gaps in the soil around the root ball that is drying out the roots. I would tamp down the soil around the plant. I would also recommend upping the watering. In addition, it could be suffering from shock. This article will help with that: https://www.gardeningknowhow.com/plant-problems/environmental/learn-how-to-avoid-and-repair-transplant-shock-in-plants.htm

If they are already accustomed to an indoor environment, then you could bring them plant inside for overwintering. Otherwise, you will have to provide adequate cold protection, such as wrapping the containers. Here is an article that you may find helpful: https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/hydrangea-winter-care-how-to-protect-hydrangeas-from-winter-cold-and-wind.htm