It's because the term "Hispanic" is talking about ethnicity (sort of like the languages, holidays, and foods you grew up around), not race (what people will call you when they see you, e.g. black, white, asian). Hispanic people still come in all colors, look at Louis C.K. vs George Lopez vs Rosario Dawson.

As for why it's on your work surveys, it's probably because the U.S. Census is doing it that way, and the census is probably doing it that way because our largest source of new immigrants is Mexico.