Undocumented migrants (aka illegals) comprise a significant percentage of that uninsured Hispanic population, but I don't have a specific figure to throw out. This group, who mostly work and pay taxes, holds down those minimum wage (or illegally sub-minimum, grey market) jobs in the construction and service industries that don't offer health insurance.

It is well documented that Blacks/African-Americans in the prison population represent a higher percentage than their proportion of the overall population. There are many contradictory studies (easily found via Google) as to why; conclusions include such things as the higher unemployment rate among young Black males, implications that Blacks (and Hispanics) are more likely to be involved in gang activity than the "white" population, the unfortunate (IMHO) propensity in the US of incarcerating people for "victimless crimes", such as using drugs, and so forth.

It should be remembered that lack of health insurance is not the same thing as lack of access to health care. Most, if not all, hospital emergency rooms are required to treat anyone who walks in the door, regardless of their medical condition or their ability to pay. There also is no question that this care is vastly inferior, over time, to that provided to people who have a family doctor who they see on a regular basis.