During my parents' era, the only people who were referred to as "Mr" or "Mrs" were white people. Blacks were referred to by their first name at best, "boy" or "gal" by standard, and "nigger" at worst. When Mary Hamilton was called to be a witness in a Mississippi court case in the early 60's, she took a stand against this demeaning practice by refusing to answer the judge unless he called her "Miss." A true product of the times, the judge refused and held her in contempt of court. The NAACP eventually took up Miss Hamilton's case, which went all the way to The Supreme Court (Hamilton v. Alabama, 1964)!

The Supreme Court ruled in favor of Miss Hamilton, forcing courts to refer to all persons, regardless of race or ethnicity, by an honorific. This practice has since passed into common usage and you'll find it common (particularly in the South) for everyone to be addressed as "Mr" or "Mrs." All of this is thanks to Miss Hamilton's stand to make us equal.

References

1. Mary Hamilton, The Woman Who Put The 'Miss' In Court". NPR. July 12, 2013
2. HAMILTON v. ALABAMA, 376 U.S. 650 (1964). Justia; visited February 2020
3. "Hamilton v. Alabama (1964)". Wikipedia; visited February 2020