I am a Mexican and have been living in the city Bremen for 3 years, no double citizenship or german parents or anything, a completely grown-up Mexican with no prior links to Germany who came here because of a love relationship (that is now over).
I have never experienced rascism or rejection whatsoever, never and I am not blond and I surely speak with an accent.
I think the reasons are:
.- I learned their behavior and talk and think like them, I don't do shit that bothers them. I abide by the rules: I buy my train tickets, bring the tablet to the counter in restaurants, don't speak loud, have courtesy, respect others, etc.
.- I speak fluent german (and learned it properly), I am not perfect but I don't go with half-assed sentences that make no sense and shit.
.- I dress up. yes, they are like "devil wears prada" Amanda priestley if by chance you look like a beggar.