Who are "brown" communities in the US?

They mean people of color other than Blacks, Native Americans, and Oriental Asians (as opposed to Asian Indians). You will find a lot of younger (under 50) Asian Indian-Americans and Pakistani-Americans who are not first generation Americans refer to themselves as Brown or a Brown community. This may just be a function of my being around more Asian Indians than Middle Easterners. Asians, in general, make up a large percentage of my neighborhood. Many Mexican-Americans (as opposed to continental Spanish) will do the same. I rarely come across Middle Eastern-Americans using the term to refer to themselves. Though, it may be more prominent in other regions of the US.