Yes, I believe healthcare has improved as much for minorities as it has for white people. Healthcare as a whole, for all people, has improved immensely. I'm convinced that healthcare no longer discriminates when it comes to color, gender, etc. In 2016 healthcare is the same for all people in the US.
Healthcare has improved over the years, and it has improved for all people regardless of their race. The fact that Stevie Wonder received poor care years ago should not be made into a race issue today. Yes, better healthcare does tend to be available for those who can afford it, but the fact that minorities are often those who cannot should not be considered a race issue. It is unfortunate that minorities are typically the ones who have financial struggles health-wise, but I don't think it's fair to say that healthcare is 'better' for whites.
As it stands, healthcare tends to improve in areas that have more money, and have more access to the latest technology. Minorities tend to live in poorer areas whose hospitals don't have the best equipment, and don't attract the best doctors. Until that changes, minority care will never catch up to white care.
I think there are several factors that contribute to the differences in the level of healthcare given to whites and minorities. One of those factors is the higher education level of the patients. Every patient needs to study up on their symptoms and advocate for themselves. The lack of higher education in certain demographics is the reason why the quality of healthcare differs.