I think it's more important how you dress than the color of your skin. If you dress in your home country's traditional clothes, you will probably experience more hostility than when you are wearing western clothes. The color of your skin will also be a factor, certainly more so than in the US, but usually hostility is based on your assumed (based on your looks) religion and values than the actual skin color. In the end, people are tribal, in rural Germany more so than in cities, and whether they accept you and how they treat you depends on whether they can relate to you.

I think language is the main factor why immigrants often will be strangers forever. Your social circle will be very limited if you don't speak German near-perfectly. But I would assume the same in the US if you don't speak English very well, and even then it's very difficult. At least that's what I have heard from Germans who moved to the US.

In bigger cities there are usually local expat communities where English is spoken, but you won't find many in rural Germany (unless you are close to a US military base or similar things). I think the best way to find them is on Facebook.

How much you will truly be accepted depends a lot on where you are. Some places, like New York or Amsterdam, are very cosmopolitan. Rural areas often a lot less so. Munich probably more than the Bavarian country side.