Confusion recognized and understood. The German documentation is a bit behind in the version number.
This “Edit” button no longer exists. It would have only shown you the extended window you have now anyway.
You have set some colors to transparent and since these are synchronized within the project, they are now gone.
Do you have a backup of the project? Then import that and it should restore the colors - i assume.
If not, and you have already published the pages, then search the source code (online) for the HEX code of the background color. You can then reassign it to a specific color field.