It turns out that the middle class diversity very closely agrees with the diversity of the overall population.

According to The Brookings Institution: "White Americans are slightly over-represented in the middle class at 59 percent compared to being 57 percent of the population. Black Americans make up 12 percent of the middle class and 13 percent of the population. Eighteen percent of the middle class identifies as Hispanic compared to 19 percent of the population. Asian Americans comprise seven percent of the middle class and seven percent of the population." (https://www.brookings.edu/blog/up-front/2020/10/30/the-middle-class-is-already-racially-diverse/)