Welcome to NGA, shawnthesheep. I think your plant is doing well. You have a hydrangea macrophylla that produces mophead blooms. These blooms consist of mostly infertile sepals (special leaves) and some fertile flowers hidden here and there. The sepals typically go through a color progression from the moment that the flower buds open until they fade and turn brown. Since these plants get shipped to florists blooming, the exact timing of all of the color changes is difficult to guess in their first year; they are forced to bloom unusually early so expect the blooms to go through the color changes earlier than they will do it in future years.
So, yes, what you are seeing in the pictures is the color progression that they go through (the plant is not dying). The exact sequence of color changes depends on the type of hydrangea and on the variety. Florists do not identify the name of varieties in the plant label so it is impossible to find out what the sequence of color changes is.... unless you just observe them on their first growing season. The duration of each of these changes can also vary but you can assume it takes close to a month or so. For example, the blooms may open pink; after a while, the pink sepals turn green; after a while, the sepals add splotches of pinks, reds and-or purples; the sepals turn brown. The browned out blooms should stay attached to the plant until February or thereabouts.
Spent blooms can be deadheaded at any time (not the same thing as pruning). Since hydrangea macrophyllas develop new "invisible" flower buds for Spring 2021 at the ends of the stems from mid summer to early Fall, try not to cut the stems now or you may be cutting off the Spring 2021 blooms. When the Spring 2021 blooms open, they will resemble small broccoli heads. See below for more info on pruning and deadheading hydrangeas:
https://plantaddicts.com/pruni...
If you will be treating this plant as an annual, you can dispose of it in the compost pile. Otherwise, consider transplanting to a bigger pot or planting it outside in the ground. They prefer morning sun (until 10-11am) or dappled sun.
Maintain the soil as evenly moist as you can and do not water/spray the leaves in order to minimize the chances of getting fungal diseases like powdery mildew or Cercospora leaf spots. Maintain 2-4 inches / 5-10 cms of organic mulch year around when planting outside.
Aphids are easily controlled with a strong stream of water from a hose, using an insecticidal soap, or an insecticide spray. Repeat per instructions in the plant labels. If using soapy water, dip a paper towel into the mixture, using it to gently wipe down the stem and leaves of the plant affected by the aphids. See below for more info:
https://www.wikihow.com/Contro...
