We're planning a 3 week trip to Germany starting August 5th but notice our US covid rate is climbing rapidly. Does anyone know what happens if the US is declared amber while we're in Germany? Would we be "grandfathered in" based on our green status at arrival or be subject to amber requirements?
See here: https://www.rki.de/DE/Content/InfAZ/N/Neuartiges_Coronavirus/Risikogebiete_neu.html
Download the English version and read " General obligation to show proof" and "Have spent time in a risk area 10 days prior to entering Germany."
The status that applies when you cross the border is the important thing. Once you have entered Germany whatever happens in the US does not affect you.
If you are in Germany when any changes are made, they won’t impact on you getting around or going places. What you may find, however, is that if the USA goes amber, then tourist demand will drop and flights will be cancelled at short notice. This happened to me last year when returning from Spain to the U.K. - my flight moved from a twice a week service to weekly.