There is one major minority group in the novel. It is the black community. As the novel progresses, it becomes clear that the black voice does not speak very loudly in Maycomb. We see this in several ways.
First, in the trial of Tom Robinson, it becomes clear as day that he did not rape or hurt Mayella Ewell, but the people would not accept solid evidence and legal reasoning. Their racism blinded them. So, even though a black man demonstrated his innocence, no one heard. This shows that the black community had little power.
We see the same point in Calpurnia's church. There were a lot of black people there, but they did not have a collective voice. They were poor and marginalized. And they were made to feel it. So, when they saw the injustices that Tom Robinson and his family had to endure, they did not protest or do anything resembling this, because they knew that they had no power.
Based on these two point, the black community only had a voice among themselves and in a few select households in Maycomb, such as Atticus' house. But even here not all were welcoming, such as Aunt Alexandra.