“Protected class” is something of a misleading piece of legal jargon; “class”, in it, means something closer to “axis of differentiation” than “group”. [0]
So, “black” is not a “protected class”, “race” is.
(This gets confusing because there is a related concept in Constitutional anti-discrimination jurisprudence of a suspect class, in which “class” does mean “group"; blacks are a suspect class—a group historically subject to discrimination, such that government actions which discriminate against them are subject to strict scrutiny—and whites are not, but both blacks and whites are protected by employment anti-discrimination law because race is a protected class.)
[0] There's a wrinkle in that “age over 40” is an asymetric “protected class” in employment anti-discrimination law.
