For changing Jupyter cell background color in PyCharm 2022.1.3, you can use:
Settings
In left navigation menu: Editor > Color Scheme > Notebooks
Color Scheme setting: Code cell background
See this example image:
PyCharm 2022.1.3 Jupyter cell background color setting in Color Schema
It makes a lot of sense, but it took me a long time to find this option as there are simply so many miniscule settings. A strategy that worked for me in the end was creating a temporary color scheme by duplicating an existing one, and than search for "background" in the settings menu, and start changing all potentially relevant values.
It made it more problematic that I believed that the PyCharm project needed to be restarted in order to apply the color scheme settings as others mentioned for previous versions, but this appeared not to be an issue for me in the end. As soon as I clicked 'Apply', it adjusted the color scheme settings also in my Jupyter notebook.